Avoid using them on the main page you register. Save them for the sub-pages. These look impressive but can defeat search engines as well as web surfers looking for content. Include keywords and key phrases in your page text. Use text links in addition to image links.
Some web surfers turn off image options in their browsers.
If you do not include text links as well as image links they will not be able to navigate your site. Some search engines robots follow only text links when processing a Web site. If your pages contain only images the content will be invisible. It covers every aspect of designing, submitting and improving sites as well as a rundown on the major search engines and which techniques each one uses to rate sites. It also warns web masters on the tricks search engines are onto such as keyword stuffing.