What is the current recommendation for providing long descriptions for complex graphics?
In HTML (Hypertext Markup Language), the
of the image element was specifically designed to allow for long
descriptions of complex images such as charts and graphs. This
contrasts with the
alt attribute, which
describes relatively simple images using a minimal amount of text. The
attribute allows authors to link to a separate page (for example,
longdesc="img1description.php") in which the image is described in
<img src="sales_march.gif" alt="march sales
graph" longdesc="march_sales.php" />
longdesc attribute was for a long time unsupported by assistive technologies, so work-around techniques (such as linking to the separate long description page using just the letter D
as link text) were used in its place. However, recent versions of most screen reader applications now support the
attribute. Screen readers typically announce the presence of a long description when
available, and provide users with the option of reading it by executing a specified keystroke.
longdesc is now supported by screen readers, it is the
recommended technique for providing long descriptions of images.
However, in using "longdesc" be sensitive to the fact that there might
still be some users with technologies that do not support it, and
consider summarizing the most critical concepts from the image within
the text content of the document. This practice helps all readers since
it reinforces the author's ideas through multiple modes of presentation.
A useful description of the appropriate use of the long description attribute can be found at Jim Thatcher's Web site in the Text Equivalents page.