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Automated License Plate Recognition (ALPR)

Automated License Plate Recognition (ALPR) is a technology that uses optical character recognition (OCR) to automatically read license plate characters.

There are two types of ALPR: stationary, which uses infrared (IR) cameras at high fixed points, and mobile, which uses vehicle-mounted IR cameras. 

Stationary cameras can be mounted on signs, street lights, highway overpasses or buildings as a cost-effective way to monitor moving and parked vehicles twenty-four hours a day. Camera software is able to identify the pixel patterns that make up a license plate and translate the letters and numbers on the plate to a digital format. The plate data is then sent to a database where it is compared in real-time to a list of plate numbers that belong to "vehicles of interest". If the system detects a match, it sends an alert to the dispatcher or other designated personnel.

Mobile ALPR software suites use multiple cameras mounted on a vehicle.  As the vehicle moves, it photographs license plates and transmits plate data to a database.  The database may be a national database or it may be created at the local level and downloaded into the vehicle's onboard computer at the beginning of each shift. If the system detects a match, the officer receives an alert on his computer. A mobile ALPR can read up to 1,000 plates per hour and cover two or more lanes of traffic at once.

Automated License Plate Recognition has many uses including:

  • Recovering stolen cars.
  • Identifying drivers with an open warrant for arrest.
  • Catching speeders by comparing the average time it takes to get from stationary camera A to stationary camera B.
  • Determining what cars do and do not belong in a parking garage.
  • Expediting parking by eliminating the need for human confirmation of parking passes.

ALPR is known by several other names, including Automatic Number Plate Recognition (ANPR), Automatic Vehicle Identification (AVI), Car Plate Recognition (CPR), License Plate Recognition (LPR), and Lecture Automatique de Plaques d’Immatriculation (LAPI).

Watch a short video demonstrating one type of mobile ALPR:

Continue reading about Automated License Plate Recognition:

Learn more about ALPR by visiting the PIPS website.

Read an article on police applications of ALPR.

Look at different types of ALPR software and hardware.

Thinking of purchasing an ALPR system?

This was last updated in January 2011

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