The Robotic Car-Tracking Eyes Of The Law

It's how the LAPD's Future Cruiser hunts for stolen vehicles. And how toll roads and municipalities across the country control traffic conditions. It reads licence plates like the Rainman counted cards.

Automated Licence Plate Recognition (ALPR) systems use optical character recognition to read the digits on vehicle licence plates. They can either be installed on stationary platforms, as they are with California's Fastrak automatic toll system, or mounted on law enforcement vehicles.

Mobile ALPR systems are comprised of four main components. Either colour video or infrared cameras are typically mounted on the roof of the cruiser and can capture the plates of oncoming, side and same-direction traffic. Some ALPR's can capture plates from oncoming vehicles travelling as fast as 190km/h, however the cameras are often limited by the ambient lighting, headlight glare and other environmentals. IR cameras were introduced to negate many of lighting/reflectivity issues early systems experienced.

Once the image has been captured, the system software uses Optical Character Recognition (OCR) to "decode" the image. OCR is the process used to convert printed text into an electronic form. You see if commonly in book digitisation, record keeping and similar applications. The OCR system runs the image through a series of algorithms to locate the plate in the image; orientate, resize, and colour-correct the plate image; then identify and analyse the individual characters.

With the plate correctly identified, the ALPR system will then run the plate number against a police database, looking for matches of known stolen vehicles, outstanding warrants, Amber Alerts, or anything else the police would like to speak with you about. The police can also store the captured images for later data mining. Some insurance companies, lenders and repo men, have access to these databases as well. Oklahoma, for example, recently rolled out an ALPR system to help eliminate uninsured motorists. They integrated it with the existing PikePass hybrid RFID/OCR toll collection system.

You can run, and you can hide. But you probably can't drive and hide for very much longer.

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