http://alistapart.com/blog/post/on-alt-text
Consider the common bio. For instance, this bio of Faruk Ateş http://alistapart.com/author/farukates
Among other elements, it contains an author photo, a page title (an h1 headline containing the author's name), and a paragraph of biographical content beginning with the author’s name. According to WCAG, it is good accessibility practice to provide alt text for those who cannot view an image. But in this case it would be bad, because a blind reader would have to listen to Faruk's name three times in a row: first, when the screen reader reads the alt text ("Faruk Ateş"), then when it reads the h1 title ("Faruk Ateş"), and lastly when it begins reading the paragraph.
Consider the common bio. For instance, this bio of Faruk Ateş http://alistapart.com/author/farukates
Among other elements, it contains an author photo, a page title (an h1 headline containing the author's name), and a paragraph of biographical content beginning with the author’s name. According to WCAG, it is good accessibility practice to provide alt text for those who cannot view an image. But in this case it would be bad, because a blind reader would have to listen to Faruk's name three times in a row: first, when the screen reader reads the alt text ("Faruk Ateş"), then when it reads the h1 title ("Faruk Ateş"), and lastly when it begins reading the paragraph.
As we crafted our templates, we discovered many places where an alt text would have been redundant, offering a blind user no new information not already provided by the page's HTML text, and merely annoying that user with needless redundancy. Markup is an art, and the soul of that art (as with all design) consists of creating the best possible experience for the user.