Yeah, I think a good example of this is thinking about something like license plate scanning.

Technically, this is not taking advantage of any public information. It is just capturing images of things happening in public. Anyone could set up a camera and capture license plates as they drive through an intersection.

So is it totally fine for a police force to scan license plates at every intersection?

The question is complicated, because the effect on people changes when you do something that is not worrisome on a small scale in an automated way at a large scale. When you add in that the people doing it have a large amount of power over people and it changes it even more.