Authenticating Locations

Okay, so suppose that somebody says they know the locations of one of the balloons, and gives you a site. How do you authenticate? Easy; go to the web; lookup the phone number of a random person who lives near the location. They'll probably do it for you, because it sounds wild and more exciting than whatever they are probably doing at that moment. If you're not sure if they'll do it; call up several people and have them check in parallel. It's very unlikely that a randomly picked person will even know about the contest. You can ask them some detail of the scene to confirm. Ideally you would tell them to ask the DARPA agent some question that is not available on the web. Of course, this only works during the contest. After the contest; it's up to documentation .. is there a photo, some kind of cryptographic proof, does the DARPA site confirm?