Google Image Search
I found this image of mine on the internet the other day by searching through Google image search. You can just drag your images into the search field, and it scours the internet for places it is being used. It's handy if you are looking to see if people are stealing your photos, or in my case to see if anybody is buying and using your shots from microstock sites.
This image was taken in May of 2013 during the herring run on the Charles River here in Watertown, MA. Apparently there aren't too many herring photos online, because a company called Evimare Fish picked it up and is using it on their homepage.