Creating Accessible Images
- Page 1: Images Introduction
- Page 2: Images that Enhance Comprehension
- Page 3: Color and Contrast
- Page 4: Text Within Graphics
- Page 5: Graphics That Cause Seizures
- Page 6: Creating Effective Alternative (
- Current page: Page 7: Long Descriptions
When to Provide Long Descriptions
Complex images, such as charts and graphs, may be too complex to describe in a brief alternative text. Alternative text is meant to be relatively short, so it would be an abuse to write more than a few words, or, at most, a few short sentences. The answer, then, is to provide a brief description of the image in the
alt attribute and then provide a longer description elsewhere.
Methods of Providing a Long Description
There are several ways of providing a long description for images. These options are listed below, in order of most preferred to least preferred:
- Provide the long description in the context of the document itself.
- Provide a link to a long description via a normal text link.
- Provide a link to a long description via the
In the context of the document itself
By putting the long description within the document where the graphic occurs, you are serving everybody, not just those with disabilities. Everyone will be able to read the long description and benefit from it. Additionally, the description is searchable (by both humans and search engines) within one web page. Here is an example of how that could be accomplished with a complex graph:
longdesc attribute, which can be added to an
<img> tag, provides access to the separate page where a long description is available. The
longdesc value must be the URL of the long description page. It should NOT contain the long description text itself. The following example is the same graph with a
longdesc attribute added:
longdesc approach is a technique recommended in both the Web Content Accessibility Guidelines and the Section 508 guidelines. However, while modern screen readers provide good support for
longdesc, browsers do not currently provide any visual indication that the image references a long description page. Many browsers do provide this information in the image details or context menu, but this is not readily apparent. For these reasons,
longdesc has been dropped from the HTML5 specification. Because the long description page is useful to all users, if longdesc is used, it should be used in conjunction with a standard link to the long description page (method #2 above).
Here is the markup for the
<img src="graph.jpg" width="526" height="353" alt="Graph of percentage of total U.S. non-institutionalized population age 16-64 declaring one or more disabilities" longdesc="media/description.htm">