A little while back I watched a police documentory about speed camaras.
The guy from the police lab claimed he hadn't came across a plate he couldn't decipher.
He then showed a few examples of the more normal reflective type plates and how he had made them ledgable and then he showed a pic taken from a gatso of a speeding car with the number plate compleatly missing.
on that pic he had still managed to trace the car. The view was from the rear of the vehicle and he had managed to get the details by tracing a sticker on the front window (through the glass and mirror image) which dipicted a garaged name. From there he said it was easy, he just contacted the garage, got a list of cars that make and model sold and then did a bit of footwork to eliminate it down to one car and that was it owner traced and busted.
That stuff might make it difficult for them but not impossible.