Yesterday, Google announced that they were completely revamping the way that image search results were displayed. TinEye is a reverse image search engine. Here’s how it works, upload an image to TinEye or paste an image url into TinEye and it will scour the web to locate other uses of that image. TinEye will give you the links to where your specified image has been used.
http://www.freetech4teachers.com/2010/07/tineye-reverse-image-search.html