You could probably get a nice point & shoot camera that would do the job. Its small & easy to use, and since the officer will be hanging onto it less chance of it getting into the bad guys hands. Since I've never had a mug shot done, I'm not sure of how it all works

A friend of mine has an older Canon point & shoot, and frankly I'm surprised its still ticking. He has dropped it numerous times on cement, fell on it while MTBing, and I think actually got it soaked on accident.