tineye
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.
Guys, heads up..the post from Baby Girl/ w pic..seeking young guys for the evening..the pic is a fake..tineye it and you'll see it used several times at different sites on the internet in various websites..word to the wise on that one.