Someone asked in class about how to add an Alt Tag to images that are generated as CSS background images. The bottom-line is that while this is an oft-used technique for presenting images, there is no way to add an Alt Tag to this kind of image. Any work-arounds do not support accessibility needs. Semantically, if an image is content, it should be in the markup.
http://www.456bereastreet.com/archive/200512/use_css_background_images_responsibly/
