Pictures are a valuable way to attract visitors to your website, because visitors search for them using Google, Yahoo and Bing image search.
When an image is placed on a page, there is a space for two tags called ALT and TITLE. These tags are displayed to the user when the mouse hovers over a picture. Both an ALT and a TITLE tag are needed because Internet Explorer supports one, and Firefox (a much better browser) supports the other. They don’t agree on which tag to use, so you should include both.
This example shows the mouse hovering over a picture and the resulting message that displays.
Google and some other search engines use the ALT tag in the same way they use the body text to rank your website in search engine result pages.