It's not possible. Whether it's a city government, judges, cops, schoolteachers, or clergy... some number of people are unethical. Trying to pretend otherwise is a source of a lot of problems. The best way to avoid it is to make it impossible, i.e. in this case don't collect the camera data in the first place. Once it is collected, it will eventually be abused no matter who has control of it.

They do, but unethical people don't announce themselves. In fact an ethical person is probably more likely to admit their faults, which usually doesn't play well in elections.