Guideline 1. Provide equivalent alternatives to auditory and visual content.
Section 508, Subpart B (Technical Standards) 1194.22
http://www.w3.org/TR/WCAG10/#gl-provide-equivalents
This guideline emphasizes the importance of providing text equivalents of non-text content (images, pre-recorded audio, video). Text equivalents can be rendered in ways so that those who have disabilities can still understand the material presented on the web page. For example, alternate text for images and other graphics can be read by a speech synthesizer for the blind or output to a Braille display for those who are both deaf and blind. The use of pictures, videos and pre-recorded audio is beneficial to some users, especially those who cannot, or have difficulty reading.
Checkpoint 1.1 - Provide a text equivalent for every non-text element.
Use “alt” for the IMG, INPUT and APPLET elements.
For complex content, use “longdesc” (e.g., to describe what’s on a chart).
Checkpoint 1.2 - Provide redundant text links for each active region of a server-side image map.
Checkpoint 1.3 - Provide an auditory description of the important information of the visual track of a multimedia presentation.
Checkpoint 1.4 - For any time-based multimedia presentation (e.g., a movie or animation), synchronize equivalent alternatives (e.g., captions or auditory descriptions of the visual track) with the presentation.
Checkpoint 1.5 - Provide redundant text links for each active region of a client-side image map.
This standard is mandatory for any organization who has government contracts, and is also important to include in the sites you develop, so that your website provides an equally enjoyable experience to any who may visit.