Effective Alt Text
http://infocentre.frontend.com/infocentre/articles/effectivealttext.html

Quinn, Anthony
Frontend Infocentre
2001

Abstract:

Good alt text can be a useful tool for enhancing the web interface. It provides supporting information, helping users gain an understanding of the structure web pages and an insight into the behaviour of key controls and interactive elements. 'ALT' is a HTML tag. It adds a short line of text to an image, usually for descriptive purposes. If you are using a mouse and you 'hover” the pointer over an image on a web page, you will notice that a short line of text appears - this is the alt text. You should also see the alt text if you switch off the images on your browser - the images have been replaced by 'placeholders” and the same short line of text which appeared when you hovered the mouse over the image.