Tineye is a delightfully simple, but clever tool. It allows you to find out where an image came from how it is being used, if modified versions of the image exist, or if there is a higher resolution version.
You can install a browser plug-in to right click and find out more. Here is one I grabbed from a recent blog post.
It could be handy for finding out just where that image came from, priming discussions around original source, attribution, copyright etc., or just really handy for finding out how far images that you’ve created as info-graphics have gone since you posted them to the internet. Either way, it’s a valuable addition to the war on ‘crap’, that I also recommend you read from Harold Rheingold’s article in Educause.