Some license plate arrangements use variations in font sizes and positioning—ANPR systems must be able to cope with such differences in order to be truly effective.More complicated systems can cope with international variants, though many programs are individually tailored to each country.However, ANPR did not become widely used until new developments in cheaper and easier to use software were pioneered during the 1990s.
The first documented case of ANPR being used to help solve a murder occurred in November 2005, in Bradford, UK, where ANPR played a vital role in locating and subsequently convicting killers of Sharon Beshenivsky.
The software aspect of the system runs on standard home computer hardware and can be linked to other applications or databases.
This equipment must also be very efficient since the power source is the vehicle battery, and equipment must be small to minimize the space it requires.
Relative speed is only one issue that affects the camera's ability to actually read a license plate.
During the 1990s, significant advances in technology took automatic number plate recognition (ANPR) systems from limited expensive, hard to set up, fixed based applications to simple "point and shoot" mobile ones.
This was made possible by the creation of software that ran on cheaper PC based, non-specialist hardware that also no longer needed to be given the pre-defined angles, direction, size and speed in which the plates would be passing the camera's field of view.
Installing ANPR cameras on law enforcement vehicles requires careful consideration of the juxtaposition of the cameras to the license plates they are to read.
Using the right number of cameras and positioning them accurately for optimal results can prove challenging, given the various missions and environments at hand.
It first uses a series of image manipulation techniques to detect, normalize and enhance the image of the number plate, and then optical character recognition (OCR) to extract the alphanumerics of the license plate.
ANPR systems are generally deployed in one of two basic approaches: one allows for the entire process to be performed at the lane location in real-time, and the other transmits all the images from many lanes to a remote computer location and performs the OCR process there at some later point in time.
ANPR technology must take into account plate variations from place to place.