Amazon.com Amazon Web Services Store: Alexa Site Thumbnail / Amazon Web Services
http://www.amazon.com/gp/browse.html/104-2713105-4524705?node=236156011&redirect=true
"The Alexa Site Thumbnail web service provides developers with programmatic access to thumbnail images for the home pages of web sites. It offers access to Alexa's large and growing collection of images, gathered from its comprehensive web crawl."