http://tineye.com/ is a new tool to help you locate your photos online. While its new and not yet as effective as I think it soon will be, its still quite useful. For stock photographers such as myself, its a way to find my images in use online. For others, it might just be useful for finding those photos that have been grabbed from your portfolio and reposted - either way, its helpful I think.

I already found one watermarked image being misused and action has been taken.