So they just ticket the car so it's basically the primary owner who has to pay? I guess that could work, in most cases the users of the car are in the same household so it's up to the family to pay the ticket. They could maybe have a shot where they get a picture of the driver and that could be sent with the ticket, though depending on windchill angle to the camera, the weather, etc wont always get a clear shot.
They'd have to figure something out for rentals though, guess the rental company could go back after whoever was the renter at the time of the ticket. I'm guessing there would be a date/time stamp on it.