In other European countries where it's also illegal to just fine the owner rather than the actual driver, the police sends an official inquiry about who was driving the car at the time. Providing false information or refusing to provide information at all is punishable by law, you have to name someone and take responsibility for the veracity of that information. The owner is legally responsible for knowing who is driving their car at all times, with the exception of the car being stolen.

In practice this just leads to a lot of penalty points or license suspensions for the 80 year old (grand)parents, or anyone who has a license but never drives.