From the Interesting-Google-Search-You-May-Not-Have-Heard-of Department

Who knew?
A reverse image search? Yes, you plug in an image into Google's image search and Google returns similar images and websites with discussion of that image. Use this search to find images that are similar, but differ in size or shape or quality. Use it also if you have questions about the identification of an image. Or if you want information about that image. Simply go to Google's image search and click on the camera at the left of the search box. You then plug in a stored image or the web address of an image. That's it. (For more info go to http://www.google.com/insidesearch/features/images/searchbyimage.html)
--RL