I did a photo scavenger hunt at AX this summer, and it was crazy.
We got into teams of 10-15, and were given a list of 15 items. I remember they were anything from the hotel sign to a picture of a starbucks cup, a corn dog, or a sign around the con. Each list was different. The hardest one for me was the Mercedes key. It would appear that there are approximately three anime fans who drive Mercedes.
People were able to just take them on their phones and show them to the judges, which was really nice. You could even do it during a two hour panel time. That is enough time for people to go, find the stuff, and come back.