Creating Text Equivalents for Images
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnacc/html/ATG_TextEquivalentsforImages.asp

Microsoft
2002

Abstract:

This article is for developers and content editors seeking to supplement the visual elements of a user interface with text equivalents. This article describes what text equivalents are, why they are required, how to create them, and the best approach to writing and editing them.