Watching the watchers
Volunteers point a spare phone at a street. It reads the vehicles that go past, keeps the government ones, and destroys everything else on the device, before anything is sent anywhere.
The photo and the plate are kept, and they become the public record. Public money, public roads, public vehicles.
The plate is destroyed on the camera itself, before anything leaves it. What reaches the server is an anonymous dot with no photo and no plate.