As far as I know there hasn't been a public source of license plate-to-owner mappings previously available. With open source license plate reader software I've seen in internet videos, it seems like a large scale leak of license plate data opens up new possibilities for private entities to track individual people's travel on public roads.
In the US, governments have been doing that for quite a while, of course.
Edit: I guess that kind of tracking is already possible if car dealerships and mechanics sell that information.
For $20, a Digital Recognition Network (DRN) customer can look up any license plate in the United States. If there is a match, the program will show the last time one of the company's cameras captured the plate, including a photo and information about when and where the photo was taken. The company sells the data to businesses, such as auto lenders, insurance carriers, repossession agents, and private investigators, but it can also be accessed by law enforcement. With more than 9 billion license plate scans in its database, it's a vast tracking tool that holds a massive amount of power. Vice recently looked deeper into the company and detailed how it works.
In the US, governments have been doing that for quite a while, of course.
Edit: I guess that kind of tracking is already possible if car dealerships and mechanics sell that information.