On a similar note, a couple of year sago the local cops were trialling a system that allowed a camera to photograph and identify number plates in the same way you describe. They had set themselves up at the entrance to a local hangour where literally thousands of cars rock up to on a saturday night. The numberplates of the cars were automatically loaded into the well known 'hoon databse' for the states police database.
Similarly they had a similar setup where they were using devices similar to speed camera on the side of the highway known for street racing, and it took the photo of every car going past. Obviously there would be normal people caught up in it all too, but when theres a pack of 100 cars in a rolling roadblock doing 40 kp/h in a 100 zone on the highway, bystanders tend to get out of the way. Not that I participate or condone such activities.
I'd love to get the source for the program they are running that identifies that charachters of the plates. That'd be good fun to muck around with.
P.S. Your posts says 300 platers hour, which is impressive. The video actually says they can scan 3000 plates an hour