There is already smart video analysis software that does this, it has been used for quite some time to look for hostile behaviour around buildings and military camps in those unfriendly countries.
Footage from a drone would just be another feed.
It is quite easy to isolate movements that go against the flow, though that does not mean it is going to be illegal activity but it helps to point out suspect behaviour and get feet on the street to check.
More and more camera coverage seems to be the future, how the privacy advocates will feel about that is a different matter entirely.