The Effect of Retro-reflectivity and Reflectance of UK Number Plates on ANPR Performance

The UK police service is one of the biggest users of ANPR technology in the world and over a number of years Police Forces have reported variances in ANPR performance based upon the retro-reflectivity properties of UK number plates. Laboratory and field-based research has been conducted with the aim of better understanding the effect of number plate component differences upon imaging systems used by law enforcement agencies for crime prevention and detection purposes. The retro reflective properties of number plates in the Infra-Red can depart significantly from visible light performance. The outcome of this work has implications for both the British Standard and for practical ANPR system design.