Web Accessibility at the University of California

Use the longdesc attribute for images with complex meaning

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The Challenge
When images are complex or provide a lot of information, use of alt text alone may not be sufficient to convey their meaning. For example, a graph showing temperature trends in Los Angeles over the last century could have an alt attribute of "Graph of Los Angeles Weather 1900-1999." The problem is that the user learns there is a graph but does not understand the content, which visually expresses temperature change across time.

Solution

• Use the LONGDESC attribute to provide descriptive information for images whose meaning cannot be conveyed with only a title. The LONGDESC attribute links to a file that contains only the descriptive information relating to the image. It can be any length necessary to accurately convey meaning.

Additional Information

• WebAIM article on the longdesc attribute
• W3C techniques for long descriptions of images