The aim of this draft is to provide best practice guidance on providing text alternatives for authors of HTML documents. Conformance requirements will be based on:
This document is for review by the HTML and Protocols and Formats working groups and is subject to change without notice. This document has no formal standing within W3C. The basis of the current content is from the text produced for Action 54 in the HTML issue tracker.
Text alternatives are a primary way for making information accessible, because they can be rendered through any sensory modality (for example, visual, auditory or tactile) to match the needs of the user. Providing text alternatives allows the information to be rendered in a variety of ways by a variety of user agents. For example, a person who cannot see a picture can have the text alternative read aloud using synthesized speech.
To determine appropriate text alternatives it is important to think about why an image is being included in a document. What is its purpose? Thinking like this will help you to understand what is important about the image for the page's intended audience. Every image has a reason for being on a page because it either provides useful information, performs a function, or enhances aesthetics. Therefore, knowing what the image is for, makes writing appropriate text alternatives easier.
Purely decorative images are visual enhancements, decorations or embellishments that provide no function or information beyond aesthetics to users who can view the images. They have no meaning in themselves and do not provide page content.
Mark up purely decorative images so they can be ignored by assistive technology with a null alt attribute (alt="") or preferably use CSS techniques. If the image isn't providing the user any informative content or enhancing greater understanding of the content, then it is appropriate for the alt text to be empty.
Context: bullets.
HTML:
<ul class="bullets">
<li>Item</li>
<li>Item</li>
<li>Item</li>
</ul>
CSS:
ul.bullets li {list-style-image:url(bullet.png);}
Context: Any decorative image in a document.
<img src="decorative.png" alt="">
Context: Specifying decorative images in the CSS document.
CSS:
#montage {background: url(images/montage.png);}
Complex data images allow sighted users to understand data and data relationships. These visual representations can convey a vast amount of non-text content.
Provide a short text equivalent that gives the user an overview of the content or helps them to understand the thrust of a relationship. In addition, for many data images it may be necessary to provide more detailed information or supplemental content in another suitable way. Often these types of images are tabular by nature, making a table a logical markup choice, because a table allows assistive technology users to interrogate and navigate the data. Other ways of conveying equivalent information for complex data images are to use the image as a link, or to provide a separate text link to a more complete text description.
Context: A graph depicting browser visits. It uses short alt text to summarize a trend with all the data in the image provided in a table.
<img src="graph.png" alt="Browser X leads visits to my site at 50 percent."
aria-describedby="t1">
<table summary="Browsers and percent of visitors to my site." id="t1">
<!-- Remainder of table -->
Context: A graph that repeats the previous paragraph in graphical form.
<p id="piedescription">According to a study covering several billion
pages, about 62% of documents on the Web in 2007 triggered the Quirks rendering mode of
Web browsers, about 30% triggered the Almost Standards mode, and about 9% triggered the
Standards mode.</p>
<p><img src="rendering-mode-pie-chart.png" alt="The majority of
documents triggered quirksmode." aria-describedby="piedescription"></p>
Context: flowchart that repeats the previous paragraph in graphical form.
<p id="flowdescription">The network passes data to the Tokeniser stage,
which passes data to the Tree Construction stage. From there, data goes to both the DOM
and to Script Execution. Script Execution is linked to the DOM, and, using
document.write(), passes data to the Tokeniser.</p>
<p><img src="images/parsing-model-overview.png" alt="parsing
model overview" aria-describedby="flowdescription"></p>
Images of pictures or graphics include visual representations of objects, people, scenes, abstractions, etc. This non-text content can convey a significant amount of information visually or provide a specific sensory experience to a sighted person.
Appropriate alt text value for a picture is a brief description, or name. As in all alt text authoring decisions, writing suitable text equivalents for pictures requires human judgment. The alt text value is subjective to the context where the image is used and the page author's writing style. Therefore, there is no single 'right' or 'correct' piece of alt text for any particular image. In addition to providing a short text alternative that gives a brief description of the non-text content, also providing supplemental content through another means when appropriate may be useful.
Context: One of many vacation trip candid photographs uploaded to a photo-sharing site. It pictures your dog, Bubbles, digging in the sand on the beach.
<figure>
<img src="1100670787_6a7c664aef.jpg" alt="My dog, Bubbles, digging in the
sand on the beach">
<legend>Bubbles traveled everywhere with us.</legend>
</figure>
Context: An image on a page explaining in general terms Rorschach inkblot personality tests. The image is an abstract freeform which is subjective to individual interpretation.
<img src="inkblot.jpg" alt="An abstract, freeform inkblot">
or
<figure>
<img src="/commons/a/a7/Rorschach1.jpg" alt="An abstract, freeform inkblot">
<legend>A black outline of the first of the ten cards in the Rorschach inkblot test.</legend>
</figure>
Context: Image of a painting inspired by a poem, on a page reciting that poem. In this case it is Waterhouse's 1888 "The Lady of Shalott" painting which was inspired by Tennyson's poem of the same name. In addition to the name provided via the alt attribute, a detailed description is provided on another page which is accessed via a link in the legend. A visible link like this can benefit not only screen reader users, but many others as well.
<h1>The Lady of Shalott</h1>
<figure>
<img src="painting.jpg" alt="The Lady of Shalott, by John William Waterhouse">
<legend><a href="description.html">Painting inspired by Tennyson's poem</a></legend>
</figure>
<!-- Full Recitation of Alfred, Lord Tennyson's Poem -->
Images of text are pictures of alphabetic or numeric textual characters.
Mark up images of text so that they will provide assistive technology with equivalent information. Provide a text equivalent word-for-word that is the same as that provided in the image. Consider the necessity of using images of text at all and try to use electronic text when appropriate. Electronic text is presentation neutral and can be rendered visually, auditorily, tactilely, or by any combination. When an appropriate markup language exists like MathML for mathematical equations, it is appropriate to use markup rather than images to convey information.
Context: Acme Company's wordmark which visually reads "Acme Company" in a fancy designed image.
<img src="wordmark.png" alt="Acme Company">
Context: An image of the word "New!".
<img src="new.png" alt="New!">
Context: Electronic text styled with CSS used instead of an image of text.
HTML:
<span class="new">New!</span>
CSS:
.new{
color:#000;
background-color:#FF9;
padding:0em 0.1em;
border:1px solid #000;
font-size: 0.8em;
}
Context: A mathematical equation
HTML:
<!-- negative example -->
<img src="pythagorean.png" alt="a2+b2=c2 (The square on
the hypotenuse is equal to the sum of the squares on the other
two sides.)">
<!-- positive example in MathML -->
<mathml>
<mrow>
<apply>
<eq/>
<apply>
<plus/>
<apply>
<power/>
<ci>a</ci>
<cn>2</cn>
</apply>
<apply>
<plus/>
<power/>
<c1>b</c1>
<cn>2</cn>
</apply>
<power/>
<c1>c</c1>
<cn>2</cn>
</apply>
</mrow>
</mathml>CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart". CAPTCHA images are used for security purposes to confirm that content is being accessed by a person rather than a computer. This authentication is done through visual verification of an image. CAPTCHA typically presents an image with characters or words in it that the user is to re-type. The image is usually distorted and has some noise applied to it to make the characters difficult to read.
Provide text alternatives that identify and describe the purpose of the non-text content, and provide alternative forms of the CAPTCHA using output modes for different types of sensory perception. For instance provide an audio alternative along with the visual image. Locate the audio option right next to the visual one. This helps but is still problematic for people without sound cards, the deaf-blind, and some low hearing people. Another method is to include a form that asks a question along with the visual image. This helps but is can be problematic for people with cognitive impairments.
Context: A CAPTCHA test which uses a distorted image of text.
<img src="captcha.png" alt="An audio challenge follows if you cannot
read the text in this image.">
<!-- audio CAPTCHA option that allows the user to listen and type the word -->
<!-- form that asks a question -->
Images of symbols are graphic representations that signify some concept, object, entity, quality, or brand. A symbol may be used to imply or represent a meaning beyond the obvious and apparent.
Markup images of symbols to identify the essence of what
they represent or their purpose. It is usually unnecessary to
describe the appearance of such an image or to identify it as a
logo. Descriptions of what a symbol looks like would typically
only be an appropriate text equivalent when it's purpose is as
an image (see images of pictures), for instance in the context
of a page explaining the visual qualities of a well designed
logo. If the symbol provides redundant or purely
decorative information, the value of the alt
attribute of the image can be null (alt="")
Context: A logo used for branding.
<h1><img src="w3clogo.png" alt="The World Wide Web Consortium (W3C)"></h1>
Context: A warning icon on a weather page about hazardous conditions.
<img src="warningicon.png" alt="warning">
Functional images are images that allow the user to 'do' things. They provide functionality. Activating or selecting a functional image causes something to happen, such as activating a link that causes a resource to be retrieved.
To provide the same functionality to the user, emphasize the action performed by the image or the link purpose. For instance, if a search button is a magnifying glass or binoculars, appropriate alt text could be "search" or "find"; not "magnifying glass", "binoculars" or "button". For navigation images, use the destination of the link as alt text. "Previous page" or "Next page" would be appropriate alt text for navigation images; not "picture of an arrow". By default, on receiving focus, a screen reader will announce to the user that it is link. So for navigation images, it is unnecessary to say "Link to previous page". "Previous page" will suffice. If a redundant text link of a navigation image is provided, the value of the alt attribute of the image can be null (alt="").
Context: Navigation link.
<a href="page1.html"><img src="leftarrow.png" alt="Previous page"></a>
Context: Navigation link with text content.
<a href="page1.html"><img src="leftarrow.png" alt="">Previous page</a>
img element" of the HTML 5 draftIt is intended that this content will be evaluated and repurposed where considered useful.
A single image can have different appropriate alternative text depending on the context.
In each of the following cases, the same image is used, yet the alt text is different each
time. The image is the coat of arms of the Canton Geneva in
Switzerland.
Here it is used as a supplementary icon:
<p>I lived in <img src="carouge.svg" alt=""> Carouge.</p>
Here it is used as an icon representing the town:
<p>Home town: <img src="carouge.svg" alt="Carouge"></p>
Here it is used as part of a text on the town:
<p>Carouge has a coat of arms.</p> <p><img src="carouge.svg" alt="The coat of arms depicts a lion, sitting in front of a tree."></p> <p>It is used as decoration all over the town.</p>
Here it is used as a way to support a similar text where the description is given as well as, instead of as an alternative to, the image:
<p>Carouge has a coat of arms.</p> <p><img src="carouge.svg" alt=""></p> <p>The coat of arms depicts a lion, sitting in front of a tree. It is used as decoration all over the town.</p>
Here it is used as part of a story:
<p>He picked up the folder and a piece of paper fell out.</p> <p><img src="carouge.svg" alt="Shaped like a shield, the paper had a red background, a green tree, and a yellow lion with its tongue hanging out and whose tail was shaped like an S."></p> <p>He stared at the folder. S! The answer he had been looking for all this time was simply the letter S! How had he not seen that before? It all came together now. The phone call where Hector had referred to a lion's tail, the time Marco had stuck his tongue out...</p>
Here it is not known at the time of publication what the image
will be, only that it will be a coat of arms of some kind, and thus
no replacement text can be provided, and instead only a brief
caption for the image is provided, in the title attribute:
<p>The last user to have uploaded a coat of arms uploaded this one:</p> <p><img src="last-uploaded-coat-of-arms.cgi" title="User-uploaded coat of arms."></p>
Ideally, the author would find a way to provide real replacement text even in this case, e.g. by asking the previous user. Not providing replacement text makes the document more difficult to use for people who are unable to view images, e.g. blind users, or users or very low-bandwidth connections or who pay by the byte, or users who are forced to use a text-only Web browser.
Here are some more examples showing the same picture used in different contexts, with different appropriate alternate texts each time.
<article> <h1>My cats</h1> <h2>Fluffy</h2> <p>Fluffy is my favorite.</p> <img src="fluffy.jpg" alt="She likes playing with a ball of yarn."> <p>She's just too cute.</p> <h2>Miles</h2> <p>My other cat, Miles just eats and sleeps.</p> </article>
<article> <h1>Photography</h1> <h2>Shooting moving targets indoors</h2> <p>The trick here is to know how to anticipate; to know at what speed and what distance the subject will pass by.</p> <img src="fluffy.jpg" alt="A cat flying by, chasing a ball of yarn, can be photographed quite nicely using this technique."> <h2>Nature by night</h2> <p>To achieve this, you'll need either an extremely sensitive film, or immense flash lights.</p> </article>
<article> <h1>About me</h1> <h2>My pets</h2> <p>I've got a cat named Fluffy and a dog named Miles.</p> <img src="fluffy.jpg" alt="Fluffy, my cat, tends to keep itself busy."> <p>My dog Miles and I like go on long walks together.</p> <h2>music</h2> <p>After our walks, having emptied my mind, I like listening to Bach.</p> </article>
<article> <h1>Fluffy and the Yarn</h1> <p>Fluffy was a cat who liked to play with yarn. He also liked to jump.</p> <aside><img src="fluffy.jpg" alt="" title="Fluffy"></aside> <p>He would play in the morning, he would play in the evening.</p> </article>
When an a element that is a hyperlink,
or a button element, has no textual content but
contains one or more images, the alt attributes must contain text that
together convey the purpose of the link or button.
In this example, a user is asked to pick his preferred color from a list of three. Each color is given by an image, but for users who have configured their user agent not to display images, the color names are used instead:
<h1>Pick your color</h1> <ul> <li><a href="green.html"><img src="green.jpeg" alt="Green"></a></li> <li><a href="blue.html"><img src="blue.jpeg" alt="Blue"></a></li> <li><a href="red.html"><img src="red.jpeg" alt="Red"></a></li> </ul>
In this example, each button has a set of images to indicate the kind of color output desired by the user. The first image is used in each case to give the alternative text.
<button name="rgb"><img src="red" alt="RGB"><img src="green" alt=""><img src="blue" alt=""></button> <button name="cmyk"><img src="cyan" alt="CMYK"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>
Since each image represents one part of the text, it could also be written like this:
<button name="rgb"><img src="red" alt="R"><img src="green" alt="G"><img src="blue" alt="B"></button> <button name="cmyk"><img src="cyan" alt="C"><img src="magenta" alt="M"><img src="yellow" alt="Y"><img src="black" alt="K"></button>
However, with other alternative text, this might not work, and putting all the alternative text into one image in each case might make more sense:
<button name="rgb"><img src="red" alt="sRGB profile"><img src="green" alt=""><img src="blue" alt=""></button> <button name="cmyk"><img src="cyan" alt="CMYK profile"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>
Sometimes something can be more clearly stated in graphical
form, for example as a flowchart, a diagram, a graph, or a simple
map showing directions. In such cases, an image can be given using
the img element, but the lesser textual version must
still be given, so that users who are unable to view the image
(e.g. because they have a very slow connection, or because they
are using a text-only browser, or because they are listening to
the page being read out by a hands-free automobile voice Web
browser, or simply because they are blind) are still able to
understand the message being conveyed.
The text must be given in the alt attribute, and must convey the
same message as the image specified in the src attribute.
It is important to realize that the alternative text is a replacement for the image, not a description of the image.
In the following example we have a flowchart in image
form, with text in the alt attribute rephrasing the flowchart in prose form:
<p>In the common case, the data handled by the tokenization stage comes from the network, but it can also come from script.</p> <p><img src="images/parsing-model-overview.png" alt="The network passes data to the Tokenizer stage, which passes data to the Tree Construction stage. From there, data goes to both the DOM and to Script Execution. Script Execution is linked to the DOM, and, using document.write(), passes data to the Tokenizer."></p>
Here's another example, showing a good solution and a bad solution to the problem of including an image in a description.
First, here's the good solution. This sample shows how the alternative text should just be what you would have put in the prose if the image had never existed.
<!-- This is the correct way to do things. --> <p> You are standing in an open field west of a house. <img src="house.jpeg" alt="The house is white, with a boarded front door."> There is a small mailbox here. </p>
Second, here's the bad solution. In this incorrect way of doing things, the alternative text is simply a description of the image, instead of a textual replacement for the image. It's bad because when the image isn't shown, the text doesn't flow as well as in the first example.
<!-- This is the wrong way to do things. --> <p> You are standing in an open field west of a house. <img src="house.jpeg" alt="A white house, with a boarded front door."> There is a small mailbox here. </p>
Text such as "Photo of white house with boarded door" would be
equally bad alternative text (though it could be suitable for the title attribute or in the legend element of a figure with this
image).
A document can contain information in iconic form. The icon is intended to help users of visual browsers to recognize features at a glance.
In some cases, the icon is supplemental to a text label
conveying the same meaning. In those cases, the alt attribute must be present but must
be empty.
Here the icons are next to text that conveys the same meaning,
so they have an empty alt attribute:
<nav> <p><a href="/help/"><img src="/icons/help.png" alt=""> Help</a></p> <p><a href="/configure/"><img src="/icons/configuration.png" alt=""> Configuration Tools</a></p> </nav>
In other cases, the icon has no text next to it describing what
it means; the icon is supposed to be self-explanatory. In those
cases, an equivalent textual label must be given in the alt attribute.
Here, posts on a news site are labeled with an icon indicating their topic.
<body> <article> <header> <h1>Ratatouille wins <i>Best Movie of the Year</i> award</h1> <p><img src="movies.png" alt="Movies"></p> </header> <p>Pixar has won yet another <i>Best Movie of the Year</i> award, making this its 8th win in the last 12 years.</p> </article> <article> <header> <h1>Latest TWiT episode is online</h1> <p><img src="podcasts.png" alt="Podcasts"></p> </header> <p>The latest TWiT episode has been posted, in which we hear several tech news stories as well as learning much more about the iPhone. This week, the panelists compare how reflective their iPhones' Apple logos are.</p> </article> </body>
Many pages include logos, insignia, flags, or emblems, which stand for a particular entity such as a company, organization, project, band, software package, country, or some such.
If the logo is being used to represent the entity, e.g. as a page
heading, the alt attribute must
contain the name of the entity being represented by the logo. The alt attribute must not contain text like the word "logo", as it is not the fact that it is
a logo that is being conveyed, it's the entity itself.
If the logo is being used next to the name of the entity that
it represents, then the logo is supplemental, and its alt attribute must instead be
empty.
If the logo is merely used as decorative material (as branding, or, for example, as a side image in an article that mentions the entity to which the logo belongs), then the entry below on purely decorative images applies. If the logo is actually being discussed, then it is being used as a phrase or paragraph (the description of the logo) with an alternative graphical representation (the logo itself), and the first entry above applies.
In the following snippets, all four of the above cases are present. First, we see a logo used to represent a company:
<h1><img src="XYZ.gif" alt="The XYZ company"></h1>
Next, we see a paragraph which uses a logo right next to the company name, and so doesn't have any alternative text:
<article> <h2>News</h2> <p>We have recently been looking at buying the <img src="alpha.gif" alt=""> ΑΒΓ company, a small Greek company specializing in our type of product.</p>
In this third snippet, we have a logo being used in an aside, as part of the larger article discussing the acquisition:
<aside><p><img src="alpha-large.gif" alt=""></p></aside> <p>The ΑΒΓ company has had a good quarter, and our pie chart studies of their accounts suggest a much bigger blue slice than its green and orange slices, which is always a good sign.</p> </article>
Finally, we have an opinion piece talking about a logo, and the logo is therefore described in detail in the alternative text.
<p>Consider for a moment their logo:</p> <p><img src="/images/logo" alt="It consists of a green circle with a green question mark centered inside it."></p> <p>How unoriginal can you get? I mean, oooooh, a question mark, how <em>revolutionary</em>, how utterly <em>ground-breaking</em>, I'm sure everyone will rush to adopt those specifications now! They could at least have tried for some sort of, I don't know, sequence of rounded squares with varying shades of green and bold white outlines, at least that would look good on the cover of a blue book.</p>
This example shows how the alternative text should be written such that if the image isn't available, and the text is used instead, the text flows seamlessly into the surrounding text, as if the image had never been there in the first place.
Sometimes, an image just consists of text, and the purpose of the image is not to highlight the actual typographic effects used to render the text, but just to convey the text itself.
In such cases, the alt attribute must be present but must consist of the same text as
written in the image itself.
Consider a graphic containing the text "Earth Day", but with the letters all decorated with flowers and plants. If the text is merely being used as a heading, to spice up the page for graphical users, then the correct alternative text is just the same text "Earth Day", and no mention need be made of the decorations:
<h1><img src="earthdayheading.png" alt="Earth Day"></h1>
In many cases, the image is actually just supplementary, and
its presence merely reinforces the surrounding text. In these
cases, the alt attribute must be
present but its value must be the empty string.
In general, an image falls into this category if removing the image doesn't make the page any less useful, but including the image makes it a lot easier for users of visual browsers to understand the concept.
A flowchart that repeats the previous paragraph in graphical form:
<p>The network passes data to the Tokenizer stage, which passes data to the Tree Construction stage. From there, data goes to both the DOM and to Script Execution. Script Execution is linked to the DOM, and, using document.write(), passes data to the Tokenizer.</p> <p><img src="images/parsing-model-overview.png" alt=""></p>
In these cases, it would be wrong to include alternative text
that consists of just a caption. If a caption is to be included,
then either the title attribute can
be used, or the figure and legend elements can be used. In the latter case, the image would in fact
be a phrase or paragraph with an alternative graphical
representation, and would thus require alternative text.
<!-- Using the title="" attribute -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="images/parsing-model-overview.png" alt=""
title="Flowchart representation of the parsing model."></p>
<!-- Using <figure> and <legend> --> <p>The network passes data to the Tokenizer stage, which passes data to the Tree Construction stage. From there, data goes to both the DOM and to Script Execution. Script Execution is linked to the DOM, and, using document.write(), passes data to the Tokenizer.</p> <figure> <img src="images/parsing-model-overview.png" alt="The Network leads to the Tokenizer, which leads to the Tree Construction. The Tree Construction leads to two items. The first is Script Execution, which leads via document.write() back to the Tokenizer. The second item from which Tree Construction leads is the DOM. The DOM is related to the Script Execution."> <legend>Flowchart representation of the parsing model.</legend> </figure>
<!-- This is WRONG. Do not do this. Instead, do what the above examples do. -->
<p>The network passes data to the Tokenizer stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokenizer.</p>
<p><img src="images/parsing-model-overview.png"
alt="Flowchart representation of the parsing model."></p>
<!-- Never put the image's caption in the alt="" attribute! -->
A graph that repeats the previous paragraph in graphical form:
<p>According to a study covering several billion pages, about 62% of documents on the Web in 2007 triggered the Quirks rendering mode of Web browsers, about 30% triggered the Almost Standards mode, and about 9% triggered the Standards mode.</p> <p><img src="rendering-mode-pie-chart.png" alt=""></p>
In general, if an image is decorative but isn't especially page-specific, for example an image that forms part of a site-wide design scheme, the image should be specified in the site's CSS, not in the markup of the document.
However, a decorative image that isn't discussed by the
surrounding text still has some relevance can be included in a page
using the img element. Such images are decorative, but
still form part of the content. In these cases, the alt attribute must be present but its
value must be the empty string.
Examples where the image is purely decorative despite being relevant would include things like a photo of the Black Rock City landscape in a blog post about an event at Burning Man, or an image of a painting inspired by a poem, on a page reciting that poem. The following snippet shows an example of the latter case (only the first verse is included in this snippet):
<h1>The Lady of Shalott</h1> <p><img src="shalott.jpeg" alt=""></p> <p>On either side the river lie<br> Long fields of barley and of rye,<br> That clothe the wold and meet the sky;<br> And through the field the road run by<br> To many-tower'd Camelot;<br> And up and down the people go,<br> Gazing where the lilies blow<br> Round an island there below,<br> The island of Shalott.</p>
When a picture has been sliced into smaller image files that are
then displayed together to form the complete picture again, one of
the images must have its alt attribute set as per the relevant rules that would be appropriate
for the picture as a whole, and then all the remaining images must
have their alt attribute set to
the empty string.
In the following example, a picture representing a company logo for XYZ Corp has been split into two pieces, the first containing the letters "XYZ" and the second with the word "Corp". The alternative text ("XYZ Corp") is all in the first image.
<h1><img src="logo1.png" alt="XYZ Corp"><img src="logo2.png" alt=""></h1>
In the following example, a rating is shown as three filled stars and two empty stars. While the alternative text could have been "★★★☆☆", the author has instead decided to more helpfully give the rating in the form "3 out of 5". That is the alternative text of the first image, and the rest have blank alternative text.
<p>Rating: <meter max=5 value=3><img src="1" alt="3 out of 5" ><img src="1" alt=""><img src="1" alt=""><img src="0" alt="" ><img src="0" alt=""></meter></p>
Generally, image maps should be used instead of slicing an image for links.
However, if an image is indeed sliced and any of the components
of the sliced picture are the sole contents of links, then one image
per link must have alternative text in its alt attribute representing the purpose
of the link.
In the following example, a picture representing the flying spaghetti monster emblem, with each of the left noodly appendages and the right noodly appendages in different images, so that the user can pick the left side or the right side in an adventure.
<h1>The Church</h1> <p>You come across a flying spaghetti monster. Which side of His Noodliness do you wish to reach out for?</p> <p><a href="?go=left" ><img src="fsm-left.png" alt="Left side. "></a ><img src="fsm-middle.png" alt="" ><a href="?go=right"><img src="fsm-right.png" alt="Right side."></a></p>
In some cases, the image is a critical part of the content. This could be the case, for instance, on a page that is part of a photo gallery. The image is the whole point of the page containing it.
How to provide alternative text for an image that is a key part of the content depends on the image's provenance.
When it is possible for detailed alternative text to be
provided, for example if the image is part of a series of
screenshots in a magazine review, or part of a comic strip, or is
a photograph in a blog entry about that photograph, text that can
serve as a substitute for the image must be given as the contents
of the alt attribute.
A screenshot in a gallery of screenshots for a new OS, with some alternative text:
<figure>
<img src="KDE%20Light%20desktop.png"
alt="The desktop is blue, with icons along the left hand side in
two columns, reading System, Home, K-Mail, etc. A window is
open showing that menus wrap to a second line if they
cannot fit in the window. The window has a list of icons
along the top, with an address bar below it, a list of
icons for tabs along the left edge, a status bar on the
bottom, and two panes in the middle. The desktop has a bar
at the bottom of the screen with a few buttons, a pager, a
list of open applications, and a clock.">
<legend>Screenshot of a KDE desktop.</legend>
</figure>
A graph in a financial report:
<img src="sales.gif"
title="Sales graph"
alt="From 1998 to 2005, sales increased by the following percentages
with each year: 624%, 75%, 138%, 40%, 35%, 9%, 21%">
Note that "sales graph" would be inadequate alternative text for a sales graph. Text that would be a good caption is not generally suitable as replacement text.
In certain cases, the nature of the image might be such that providing thorough alternative text is impractical. For example, the image could be indistinct, or could be a complex fractal, or could be a detailed topographical map.
In these cases, the alt attribute must contain some suitable alternative text, but it may
be somewhat brief.
Sometimes there simply is no text that can do justice to an image. For example, there is little that can be said to usefully describe a Rorschach inkblot test. However, a description, even if brief, is still better than nothing:
<figure> <img src="/commons/a/a7/Rorschach1.jpg" alt="A shape with left-right symmetry with indistinct edges, with a small gap in the center, two larger gaps offset slightly from the center, with two similar gaps under them. The outline is wider in the top half than the bottom half, with the sides extending upwards higher than the center, and the center extending below the sides."> <legend>A black outline of the first of the ten cards in the Rorschach inkblot test.</legend> </figure>
Note that the following would be a very bad use of alternative text:
<!-- This example is wrong. Do not copy it. --> <figure> <img src="/commons/a/a7/Rorschach1.jpg" alt="A black outline of the first of the ten cards in the Rorschach inkblot test."> <legend>A black outline of the first of the ten cards in the Rorschach inkblot test.</legend> </figure>
Including the caption in the alternative text like this isn't useful because it effectively duplicates the caption for users who don't have images, taunting them twice yet not helping them any more than if they had only read or heard the caption once.
Another example of an image that defies full description is a fractal, which, by definition, is infinite in complexity.
The following example shows one possible way of providing alternative text for the full view of an image of the Mandelbrot set.
<img src="ms1.jpeg" alt="The Mandelbrot set appears as a cardioid with its cusp on the real axis in the positive direction, with a smaller bulb aligned along the same center line, touching it in the negative direction, and with these two shapes being surrounded by smaller bulbs of various sizes.">
In some unfortunate cases, there might be no alternative text available at all, either because the image is obtained in some automated fashion without any associated alternative text (e.g. a Webcam), or because the page is being generated by a script using user-provided images where the user did not provide suitable or usable alternative text (e.g. photograph sharing sites), or because the author does not himself know what the images represent (e.g. a blind photographer sharing an image on his blog).
In such cases, the alt attribute's value may be omitted, but one of the following
conditions must be met as well:
title attribute is
present and has a non-empty value.img element is in a figure element that contains a legend element that contains
content other than inter-element whitespace.img element is part of the only paragraph directly in its section, and is the only img element without an alt attribute in its section, and its section has an associated
heading.Such cases are to be kept to an absolute
minimum. If there is even the slightest possibility of the author
having the ability to provide real alternative text, then it would
not be acceptable to omit the alt attribute.
A photo on a photo-sharing site, if the site received the image with no metadata other than the caption:
<figure> <img src="1100670787_6a7c664aef.jpg"> <legend>Bubbles traveled everywhere with us.</legend> </figure>
It could also be marked up like this:
<article> <h1>Bubbles traveled everywhere with us.</h1> <img src="1100670787_6a7c664aef.jpg"> </article>
In either case, though, it would be better if a detailed description of the important parts of the image obtained from the user and included on the page.
A blind user's blog in which a photo taken by the user is shown. Initially, the user might not have any idea what the photo he took shows:
<article> <h1>I took a photo</h1> <p>I went out today and took a photo!</p> <figure> <img src="photo2.jpeg"> <legend>A photograph taken blindly from my front porch.</legend> </figure> </article>
Eventually though, the user might obtain a description of the image from his friends and could then include alternative text:
<article> <h1>I took a photo</h1> <p>I went out today and took a photo!</p> <figure> <img src="photo2.jpeg" alt="The photograph shows my hummingbird feeder hanging from the edge of my roof. It is half full, but there are no birds around. In the background, out-of-focus trees fill the shot. The feeder is made of wood with a metal grate, and it contains peanuts. The edge of the roof is wooden too, and is painted white with light blue streaks."> <legend>A photograph taken blindly from my front porch.</legend> </figure> </article>
Sometimes the entire point of the image is that a textual
description is not available, and the user is to provide the
description. For instance, the point of a CAPTCHA image is to see
if the user can literally read the graphic. Here is one way to
mark up a CAPTCHA (note the title attribute):
<p><label>What does this image say? <img src="captcha.cgi?id=8934" title="CAPTCHA"> <input type=text name=captcha></label> (If you cannot see the image, you can use an <a href="?audio">audio</a> test instead.)</p>
Another example would be software that displays images and asks for alternative text precisely for the purpose of then writing a page with correct alternative text. Such a page could have a table of images, like this:
<table> <thead> <tr> <th> Image <th> Description <tbody> <tr> <td> <img src="2421.png" title="Image 640 by 100, filename 'banner.gif'"> <td> <input name="alt2421"> <tr> <td> <img src="2422.png" title="Image 200 by 480, filename 'ad3.gif'"> <td> <input name="alt2422"> </table>
Notice that even in this example, as much useful information
as possible is still included in the title attribute.
Since some users cannot use images at all
(e.g. because they have a very slow connection, or because they
are using a text-only browser, or because they are listening to
the page being read out by a hands-free automobile voice Web
browser, or simply because they are blind), the alt attribute is only allowed to be
omitted rather than being provided with replacement text when no
alternative text is available and none can be made available, as
in the above examples. Lack of effort from the part of the author
is not an acceptable reason for omitting the alt attribute.
Laura Carlson, Josh O'connor, Gez Lemon, Gregory Rosmaita, Ian Hickson.