Techniques for WCAG 2.0

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H45: Using longdesc


HTML and XHTML documents that include images that cannot be described in a short text alternative.

This technique relates to:

User Agent and Assistive Technology Support Notes

Voiceover 4.0, NVDA 2012, Orca 2.32.0, and Zoomtext 10.0 (and their earlier versions) do not support the longdesc attribute. Versions of JAWS earlier than JAWS 4.01 and versions of WindowEyes earlier than WindowEyes 4.5 do not support this attribute, but later versions do.


The objective of this technique is to provide information in a file designated by the longdesc attribute when a short text alternative does not adequately convey the function or information provided in the image. The longdesc attribute is a URI, the target of which contains a long description of the non-text content.


Example 1

Example Code:

<p><img src="chart.gif" alt="a complex chart" longdesc="chartdesc.html"/></p>



  1. Check that the img element has a longdesc attribute.

  2. Check that the value of the longdesc attribute is a valid URI of an existing resource.

  3. Check that the content at the target of that URI contains a long description describing the original non-text content associated with it.

Expected Results

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.

Techniques are Informative

Techniques are informative—that means they are not required. The basis for determining conformance to WCAG 2.0 is the success criteria from the WCAG 2.0 standard—not the techniques. For important information about techniques, please see the Understanding Techniques for WCAG Success Criteria section of Understanding WCAG 2.0.