Don't use drones or CCTV.

Crowd source the security.

I the modern world we don't take pictures of people we don't know, its considered rude. We let the state do it because somehow they are not human. However if it became the norm that 50% of a crowd of people took pictures of everybody else then you have a massive record to call upon when a crime happens. If nothing happens then the jigsaw is incomplete and privacy is maintained.