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A text equivalent
for every non-text element shall be provided (e.g., via alt tags, "longdesc,
or in element content). ALT Tags -- Dos and Don'ts
Why: ALT tags offer the only method for screen readers to render images. They also act as descriptive place-holders when users turn-off images in their browsers (as users of slow internet connections frequently do). How: Most web authoring tools (e.g. Dreamweaver, FrontPage) allow you to set the accessibility options so the program automatically asks you to enter an ALT tag when an image is inserted. If your editor does not have this option, you must add the alt="description" attribute to the <IMG> element in your HTML code.
Why: Images used for spacing or aesthetics are not needed to understand the content of the page. By including a descriptive ALT tag for these images, you are adding unnecessary clutter to your pages. However, an empty ALT tag signals to the screen reader to "skip" the image and not identify it. If there is NO ALT tag, the screen reader will still say "graphic" or "image." How: Some web editors only allow you to either create a descriptive ALT tag or no ALT tag. Since inserting an empty alt tag (ALT="") is different from having no ALT tag, you may have to directly edit the <IMG> element in your HTML code to create an empty ALT tag.
Why: What an image looks like or how it is arranged is frequently less important that the function that the image has on the page: a link, an example, a highlight. When you are unable to describe the function of the image in less than 150 characters, use the LONGDESC attribute to give users more time to review your description. How: Keep it <150 characters when possible. Use the LONGDESC attribute for longer descriptions. Focus on the purpose of the image rather than the characteristics of the image. If you find yourself saying "this image is just fun" or "this image is just pretty", consider using an empty ALT tag for that image. Get more help with ALT tags for Images, visit All Things Web: "The Art of ALT"
Long Descriptions (LONGDESC) -- Dos and Don'ts
Why: Using the LONGDESC attribute requires you to put the full and detailed description on a separate HTML page, where users will have time to review it and can easily come back to the description. The long description should be used when detailed explanations, transcripts, or other lengthy descriptions are needed to fully comprehend the graphic or image. How: Create a separate page containing the long description. Include both the ALT and LONGDESC attribute in your <IMG>, and include the URL to the long description page as the value of the LONGDESC attribute. For example: <IMG src="cartoon.gif" alt="a Calvin and Hobbes cartoon" longdesc=/images/calvin-writing.htm>
Why: Browser support for the LONGDESC attribute is not yet extensive. Therefore, designers must also use the older solution of the D-link. How: Immediately following (to the right) of the image, include a link to the long description page. Make the link text a "D." Example: <IMG src="cartoon.gif" alt="a Calvin and Hobbes cartoon" longdesc=/images/calvin-writing. Htm><A href="/images/calvin-writing.htm>D</a>. You may make this D-link invisible or transparent using style sheets or other methods. See this method in action: WAC Best Practices Tutorial: Images.
Why: Linking to a page containing the long description interrupts the flow of the current page content and may become tedious if several graphs or charts requiring long descriptions are on a single page. Using an in page caption helps not only visually impaired users, but all users who may otherwise have difficulty interpreting the image, graph, or chart. How: Whenever possible, place the caption or description before (above or to the left) of the image it describes. This insures that screen readers read the description before reaching the image. Captions may be identified by formatting or may be included in-line with the other text on the page. Get more help with Long Descriptions , visit W3C's "7.2 Long descriptions of images."
Alternative Text for MultimediaSee also: Standard 2 -- Synchronization.
Why: A transcript represents a true "alternate format" of video that does not require special software (video viewer) to access. Captions help make video more accessible, but still depend on the accessibility of the player. How: Use the same text used in captioning to create a transcript. The transcript may also include more thick description than the captions would (e.g. descriptions of the scene, graphics displayed, and other visual elements important to comprehension). Top
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