Startup Idea : Automatic geolocator for photos without GPS info

I travel a lot and I have plenty of pictures. I wanna create a world map from them. Unfortunately, I don't have a camera with GPS module so I cannot locate my photos. I bet there are very similar pictures from most of the places somewhere else on the internet already geolocated (like Panoramio etc.). Could be cool if anyone comes up with service that match my photos with the real places based on similarity with already located pictures. I know it won't catch all of them but at least some portion would be really helpful.