TinEye is a reverse image search engine built by Idée currently in beta. Give it an image and it will tell you where the image appears on the web.
Source: www.tineye.com
This is a great website – upload an image, or paste the URL address and it’ll find where else the image is being or has been used. Super for anyone teaching digital graphics checking authenticity, great for photographers ensuring their copyrights and just worth a look if you are into your imagery.