tags are used to provide Internet users with a description
of an image on a web page. You'll see the ALT tag when
you hover your mouse over the image. These tags are
useful if an image hasn't loaded or if the browser has
images turned off.
an example of image that hasn't loaded:
ALT tags increase the usability of a web site, they
play a part in the assessment that a search engine will
perform of the web page. The search engines that incorporate
ALT tags into their search algorithms are Google, Alta
Vista and Teoma.
text is added to an image like this:
pop-up text is the ALT text">