If you're a conscientious and upstanding webmaster who cares about the rights of rights holders as much as you wish others cared about yours, try http://www.tineye.com/ This tool lets you look up an image you wish to use on your site so you can get permission. ALso, it lets you check if someone else lifted your stuff so you can enforce your rights.
Resource: http://www.tineye.com/
Archive of my posts: http://twitter.com/askmr5dollar
Resource: http://www.tineye.com/
Archive of my posts: http://twitter.com/askmr5dollar