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License Plate Recognition Systems – What Citizens Should Know

License Plate Recognition

License Plate Recognition technology, or LPR for short, has already made a big impact on the law enforcement field. A number of police forces already use this powerful technology to scan the license plates of cars passing by a given location, and the ability to scan thousands of license plates has already led to the apprehensions of murderers, rapists, child predators and other dangerous criminals.

By scanning every passing car and cross-referencing the license plate information with various law enforcement databases, police can find the bad guys without inconveniencing the rest of us or putting our privacy at risk. This emerging technology is still in its infancy, but it is likely to be an even more important law enforcement tool in years to come.






What is License Plate Recognition?

In many ways License Plate Recognition is just what the name implies – namely technology that is able to scan license plates and identify vehicles based on that information. The technology has a number of important applications, including traffic control, access control and law enforcement.

Gated Communities and LPR

One of the most practical uses for License Plate Recognition is in gated communities and other limited access locations. As the car approaches the gate, the license plate reader scans the information and compares it to a predetermined list of those with permission to enter the facility. If there is a match, the gate opens automatically – if the license plate does not match an authorized user entry is denied.

This technology can be used in a number of different locations, including sensitive government buildings where security is a paramount concern, laboratories where access needs to be restricted for public safety reasons and intelligence agencies where access is restricted to those with a legitimate need to enter the facility.

Traffic and LPR

License Plate Recognition technology is rapidly growing in acceptance amount traffic control organizations and municipalities. Unlike the technology used on toll roads around the country, an implementation of LPR technology does not require a separate transponder or reader. Since the information needed is already on the car, the LPR can simply read the license plate number and perform the required action. This emerging technology has applications in areas like speed control, red light running and accident scene reconstruction.

LPR systems use a special camera and special lighting to take a picture of the front or back of the car. Once the images have been captured image processing software analyzes the data to extract the license plate information. The data used is then collected and used for various functions, including traffic control, law enforcement and granting access to restricted areas.

Retention of Data

One of the chief advantages of the LPR system over other forms of vehicle surveillance is the fact that the images can be stored and retained. This allows law enforcement agencies to track possible criminal suspects as they move around a given location. The technology can also be used to track and recover stolen vehicles, since an additional camera can be trained on the interior of the car and used to identify drivers and passengers.

Recognizing an LPR System

While the term LPR is widely used throughout the law enforcement industry, the technology is also known by a number of alternative names. If you hear someone talking about Car Plate Recognition, Car Plate Reader (CPR), Automatic Vehicle Identification (AVI), Optical Character Recognition for cars (OCR), or Automatic Number Plate Recognition (ANPR), they are actually talking about License Plate Recognition. The names may be different, but the underlying technology is still the same.

License Plate Recognition technology can be used in a number of different ways to control access to secured areas and sensitive locations. The system can even be configured to display the license plate number and the name of the driver as each vehicle is granted access. This vehicle identification information can then be stored in a centralized database, where it can be used for everything from assessing traffic patterns to reconstructing a crime scene.

It is important to keep in mind that while LPR technology is universal, the actual reading of the plates is specific according to the country. That is because the license plates used in each country can have a different size, shape and color, and in order for License Plate Recognition software to work properly it needs to be configured for the proper type of plate. Once the system knows the size and shape of the license plate the software will be able to scan the appropriate area and use its built in recognition software to create the images.

The LPR Image

The LPR image itself is rendered in grayscale, using the standard 256 levels of gray. These shades range from black, which is represented by the number 0, to white, which is represented as 255. Each shade in between these two extremes has its own number, and those grayscale images are processed by the recognition software, which actually reads the plate.

The processors involved start off with information about where the plate is located on the vehicle. The software then zooms in on the plate to read the small details and finally determine the actual plate number. Thanks to the power of the processors involved, the entire process, from taking a picture of the license plate to rendering the final license plate number, takes place in a matter of seconds.

Is LPR Reliable?

As with any new technology, LPR has suffered from its fair share of failures. Early License Plate Recognition systems often had abysmally low rates of recognition, and in order to be useful these systems needed to be augmented by human operators. Early systems were also easily confused by common things like sun glare on the plate and the glare of oncoming headlights. Early systems also suffered from poor quality readouts, and it was often difficult for even experienced law enforcement personnel to read a plate accurately.

LPR technology has come a long way since those early days, and newer systems are both more reliable and easier to use. These days LPR systems are already in place in a number of locations, from secured parking garages and government facilities to high end gated communities. In addition to the basic License Plate Recognition technology, these systems often include practical add-ons like ticket dispensers, card readers and lighted displays.

What Does an LPR Unit Include?

While the uses of LPR technology vary quite a bit, every LPR installation will have the same basic elements. The License Plate Recognition system will include one or more cameras to take images of the front and rear of each car passing through the system. The system will also include some form of lighting that makes it possible to read the license plate even in dim light. Many LPR installations will use infrared illumination. In addition to being very practical, infrared illumination also has the advantage of being invisible to the driver, certainly an important benefit for law enforcement installations.

The LPR installation will also include something known as a frame grabber. This frame grabber allows the software to read the image information captured by the camera. In addition, the LPR installation will include a computer that controls the system, reads the captured images and performs the identification of the license plate. In addition to the computer itself, the installation will include specialized software that is able to perform the plate recognition and compare it to a given database. The information recorded from the plates can be recorded to a local database or sent over a network.

How Does the License Plate Recognition System Work in the Real World?

In order to better understand how this technology is used in real world situations, it is helpful to take a look at a typical scenario. In a typical installation of LPR, the vehicle triggers the recognition process by driving over a vehicle sensor embedded in the ground. As the vehicle approaches the entrance gate to the building, parking garage or other secured structure, the vehicle sensor is triggered and the plate is illuminated with infrared light. This infrared light is invisible to the driver, so chances are he or she does not know that the license plate information is being captured.

An image of the vehicle’s license plate is captured by the camera and processed by the frame grabber. Specially designed software algorithms are used to enhance the image and make it more recognizable. After the image of the plate has been rendered by the software, the plate number is compared to a database that contains a list of vehicles authorized to enter the facility. If the plate number matches a vehicle on the authorized list, the gate lifts and the vehicle is permitted to enter. If the plate read does not match an entry in the database the vehicle is refused entry and the driver must leave the area. After an authorized vehicle has entered the facility, the gate closes and waits for the next vehicle to drive over the sensor plate in the ground.

How is LPR Technology Used?

License Plate Recognition technology is used in a number of different ways, including

  • Parking enforcement – with an LPR system drivers who have prepaid for parking at an area garage can automatically be admitted, while other drivers are turned away.
  • Border control – vehicles that cross the border on a regular basis can be entered into a special database and given priority treatment at border crossings. This use of LPR technology may be able to significantly shorten lines and reduce wait times at busy crossing points.
  • Traffic monitoring – traffic studies are necessary to make sure area roads are sufficient to handle the current load, and LPR technology can help those traffic studies by providing an accurate count of the number of vehicles on a given roadway. LPR technology can even be used to monitor a vehicle’s speed between given points and give tickets to speeding drivers.

As you can see, License Plate Recognition is a very promising technology for a number of reasons. Many of the aspects of this emerging technology are already in use, and many more features are expected to be rolled out as the technology matures and the quality of the captured images gets better and better.