London Congestion Charge : This is an interesting Wikipedia article about the “congestion charge” levied on vehicles entering the busiest zone in Central London. Apparently traffic was so bad here, that they charge people $9 US for a day pass to drive in it.
Those sneaky Brits are too smart for mere tollbooths for enforcement:
Two hundred and thirty CCTV-style cameras, of which 180 are installed at the edge of the zone, record a stream of video of roads in the zone. There are also a number of mobile camera units which may be deployed anywhere in the zone.
It is estimated that around 98% of vehicles moving within the zone will be caught on camera. The video streams are then transmitted to a data centre located in Central London where a computer system equipped with Automatic Number Plate Recognition (OCR) software deduces the registration plate of the vehicle.
Here’s another good article about the technology. I think the Brits have pioneered this just because the numbers on the license plates are so big.