What are the disadvantages of automatic number plate recognition?
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Automatic License Plate Recognition (ANPR, see also other names below) is a technology that uses optical character recognition on images to read the license plate of the vehicle. You can use existing closed circuit television, road rules enforcement cameras or cameras designed specifically for the task. The ANPR is used by police forces around the world for law enforcement purposes, including to check if a vehicle is registered or licensed. It is also used for electronic toll collection on pay-per-use roads and as a method of cataloging traffic movements, for example, by motorway agencies. Automatic recognition of the number plate can be used to store the images captured by the cameras as well as the license plate text, with some configurable to store a photograph of the driver. The systems usually use infrared illumination to allow the camera to take the photograph at any time of the day. ANPR technology must take into account plate variations from one place to another.
Concerns about these systems have centered on fears of privacy that the government traces citizens' movements, misidentification, high error rates, and increased public spending. Critics have described it as a form of mass surveillance.
There are a number of potential difficulties that software should be able to cope with. These include:
• Poor file resolution, usually because the board is too far away but sometimes results from the use of a poor quality camera.
• Blurred images, particularly motion blur.
• Poor illumination and low contrast due to overexposure, reflection or shadows.
• An object that obscures (part of) the plate, very often a tow bar, or dirt on the plate.
• Read plaques that are different in the front and rear due to towed trailers, campers, etc.
• Vehicle lane change in the camera's viewing angle during the reading of the plate.
• A different source, popular for vanity plates (some countries do not allow such plates, eliminating the problem).
• Avoidance techniques.
• Lack of coordination between countries or states. Two cars from different countries or states may have the same number but different plate design.