Todd Schwartz on Bing's Blog is giving some tips on optimizing the photos and graphics for image search. He is talking about optimization techniques recommended by the Bing's top image developer. Here are some:
Alternative Image Text (alt text) Matters
If you want better optimization, properly describe the photos with alternative text tags and make sure that the text within images is also optimized.
Appropriate Naming of Image Files
If the file name describes the image properly, it will have improve relevancy.
Watch Frame Breaking
If the site attempts to break frames, the search engine will find it difficult to display the image correctly in the search. Test your site against the search engines.
Schwartz also talked about the importance of image search at the Image Search Session held at SES San Jose a few weeks ago. He also shared the image search data from comScore for June 2009.