The ALT text of an image tag is used to describe a graphic for those users
who surf with the graphics turned off. It is also useful for those who are
sight impaired and have software that reads the contents of Web pages to them.
To see ALT text on a page, put your cursor over an image. If there's ALT text,
it will show up in a box beside the image. Some search engines will index the
contents of ALT text and use it when determining relevancy and ranking.
However, be sure to describe the image first while also including your keyword
phrase. Use moderation by using your keyword phrase only one time in the ALT
text of an image tag.
Don't use the ALT text area as a place to stuff your keywords since this is
considered spam by the search engines.
Example:
<IMG SRC="WineLogo Image-299X77.gif" ALT="Italian
wine, Australian red wine, New Zealand white wine pictured in a hamper">