A friend of mine, David Lussey (who founded Softswitch/Peratech) made an aerial photography rig out of a large, slow model aircraft about 20 years ago. He mounted a standard 35mm Nikon F (rugged and cheap second hand at the time) with a 200 exposure bulk film pack and used a timer to trigger exposures at preset intervals such that at the model's altitude of about 200ft he got 50% frame overlap. It was mainly used for photographing large houses and grounds Kites were tried but without success (never enough wind when you needed it and a tenancy to crash) as were blimps (too much wind for them). Model helicopter was useless as far too much vibration and also difficult to fly. The large slow model was the best choice.
For commercial aerial photography from model aircraft CAA authorisation is required
I would have thought the same idea - a large, stable, model with a downward looking digital camera , big memory card and timer would work as well. GPS info could locate the aircraft track either by using a stand alone gps as a track logger or using a camera with a GPS interface to record position from a stand alone receiver to EXIF data on each image.
The new Nikon P6000 weighs about 8 oz and has a built in GPS receiver as well as IR remote trigger so looks idea for the job.
The advantage of keeping the images in the aircraft is of course vastly better image quality than you could achieve on a downlink. With about 250 photos per battery that would give more than enough coverage and the geotagging would enable you to know the aircraft position when the photo was taken.
Assume