It's not easy. Not easy at all. You might look up research on it. I can't remember who it was - either Google or Microsoft or both - that was trying to look at a huge database of online photos and identify were they were taken. Like imagine if you could look at any arbitrary photo and determine if it was taken in San Diego, at the Grand Canyon, at the Statue of Liberty, or at the Coliseum. It's pretty sophisticated image analysis done by teams of very very smart people. Try to find their research - I forget what the project was called. It might have been PlaNet or PhotoStory or Mobile Video Search or IGroup
But good luck.
