Gary Pool has some good SEO tips for image search engines. Excerpts:

• If you have a series of related images, use descriptive variations.
  • 1. “Google’s Ivan Kostoylevsky logo”
  • 2. “Google’s Unexplained Phenomenon logo”
  • 3. “Google’s 400th Anniversary of Galileo’s First Telescope logo”
• Use images that will reduce to thumbnails and remain recognizable
  Quality pictures with high contrasts and clear, bright, colors always work best. The search engines generate small thumbnails to be included in search results, and you want images that will actually be recognizable is that small size.
• Adding descriptive text in the vicinity of the picture is a good thing
  In determining what the picture is actually depicting, the search engines will examine the text adjacent to the image.
• Don’t use frame breaking code
  “Watch frame breaking – Sites that attempt to break frames make it more difficult for the image to display correctly within search. Make sure you’re testing your site against the search engines.”