TinEye – Reverse Image Search Engine
http://www.tineye.com/

TinEye is a reverse image search engine. You can submit an image to TinEye to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution versions. TinEye is the first image search engine on the web to use image identification technology rather than keywords, metadata or watermarks. It is free to use for non-commercial searching. TinEye regularly crawls the web for new images, and we also accept contributions of complete online image collections. To date, TinEye has indexed 1,800,781,909 images from the web to help you find what you’re looking for. This has been added to the tools section of Research Resources Subject Tracer™ Information Blog. This has been added to World Wide Web Reference Subject Tracer™ Information Blog.