jgeating:
ubiquity offers essentially a wifi module called the bullet that is essentially just a standard wireless network for long ranges and high data transfer rates. Picture clarity and resolution are very important because the images will be analyzed using openCV to find various glyphs on the ground. This is the reason why we decided not to go with video and pictures instead. Assuming we went through USB, are you saying the arduino serial communications would bottleneck the process? There are publically available serial protocols for DSLRs I believe, but I imagine either the arduino or the ethernet shield (which the bullet plugs into), would slow things down majorly.The flow I should have put in the post, which I don't even know if it is compatible:
Camera>USB>Arduino serial port>ethernet shield>bullet wifi device>ground antenna>ground computer
It depends on the DSLR. My Olympus cameras don't have a public protocol for uploading. I haven't done the math, but from what I've read in other posts, the Arduino is just to slow to keep up with the data stream. I know it can't keep up with video unless you reduce the picture size to something like 160x120 black and white images.
If the bullet is just standard wireless, and your DSLR takes SD cards, I would look into Eyefi cards. These are used like memory cards, but can communicate via wifi networks to upload the photos as you take them. Unfortunately, they don't support CF cards, and using a CF->SD card adapter either doesn't work, or it reduces the wifi range drastically. I would imagine the heavier DSLRs may provide shielding, and you may need to get the wifi receiver antenna close to the camera.
However, the above is guesswork, and such. You won't know until you actually try it.