Did you know that digital cameras include tracking information on exactly what camera took the picture? It is public information. You can call it up in Adobe Photoshop and look at it. (Which, by the way, also stores information on who editing the image, but in encrypted format so Adobe can spy on you and make sure you are using a licensed version).
Now, has your digital camera been lost or stolen?
Put the two together and you have a new Web service to offer people, the Stolen Camera Finder.