Please also see my current work at The Enabled Web.
Situations, techniques, and tests are from the W3C WCAG 2.0 Draft. These examples also map to Section 508 paragraph 1194.22(a); please see our Mapping Section 508 to WCAG 2.0 page for further information.
G94: Providing short text alternative for non-text content that serves the same purpose and presents the same information as the non-text content using a short text alternative technique listed below
3. H37: Using alt attributes on img elements (HTML)
<img src="tj-name.gif" alt="Tom Jewett, home page" height="50" width="173" />
<img src="tj-pix2.jpg" alt="Photograph of Tom outside Brotman Hall, 2001" height="209" width="173" />
Note: (9/20/2013) With CSS3, there is no longer any reason for an image that contains only text. My current personal web site biography page has the same layout as the above illustration, but only the photograph is an image with alt-text. Text as part of a graphic logo still makes sense, though.
G95: Providing short text alternatives that provide a brief description of the non-text content using a short text alternative technique listed below AND one of the following techniques for long description:
G74: Providing a long description in text near the non-text content, with a reference to the location of the long description in the short description
red, green, blue
yellow = red + green,
white = red + green + blue (#FFFFFF)
<img src="rgb.jpg" alt="RGB color diagram, description follows" height="256" width="256" />
G73: Providing a long description in another location with a link to it that is immediately adjacent to the non-text content
<img src="association-custorder.gif" alt="Customer-order class diagram" height="149" width="357" />
Remove, hide, or mask the non-text content
Replace it with the text alternative
Check that nothing is lost (the purpose of the non-text content is met by the text alternative)
If the non-text content contains words that are important to understanding the content, the words are included in the text alternative
Check #3 is true. If the non-text content contains words that are important to understanding the content, check #4 is also true.