What about a system where users can earn points for rating submitted images?
If a picture for a certain airport is uploaded, it's not immediately shown at that airport. Instead, it enters a pool of pictures. Users can enter a page where they're presented with random pictures in this pool with two buttons beneath them. Good or bad.
Images need to be rated by a certain number of users, let's say 100 users. Out of those 100 users, 90 must rate them good in order for the picture to be accepted. If it doesn't make 90 positive ratings, the image is discarded. That should filter out most unwanted pictures. The few remaining can always be deleted by an admin, but it won't be many.
Users can be rewarded for rating pictures, they could get for example money or reputation for it. No large amounts, but each bit helps.