How do surveillance cameras deter crime?

The criminal will be scared that the police will identify him/her and hunt him/her down so he/she is not sure whether to take the risk.

That's not to say they don't turn them on though. It's true that they are most efficient through functioning as a scare tactic, but hidden cameras are used as well in which case a perpetrator's identity is revealed, rather than preventing them from doing it in the first place. A camera in the open is subject to catching only whatever someone who sees it wants to let it catch. A hidden camera sees it all, as a suspects behavior is not affected by what they don't know is there.