Working towards an international ANPR Standard — An initial investigation into the UK standard

This paper examines the use of the UK National AC PO ANPR Standard (NAAS) as the "de facto" technical standard applied in many international countries. It considers the requirement for a standard and examines the effectiveness of the current NAAS and questions its fitness for purpose. The need for accuracy is discussed in terms of both tackling terrorism, serious crime and other law enforcement investigations alongside the need to protect citizens from unwarranted infringement of their privacy as a result of ANPR misreads. The causes of inaccurate ANPR read data are examined in more detail and recommendations made as to how improvements could be introduced to minimise the risk of misreads and "missed" reads. This paper recommends future parameters of measurement and provides examples of gaps between the current standards and existing legislation. Laboratory and field testing was carried out to gain a better understanding of the factors that affect the performance of ANPR systems. These tests were carried out under a variety of weather and lighting conditions. The results of this work have led to further testing to better understand the optimum conditions for number plate capture by a variety of ANPR systems. Additional testing has been carried out using "hard to read" number plates with a number of differing characteristics such as illegally spaced characters, illegal fonts, screw caps that interfere with infrared imaging and defects in the construction of the number plate itself (whether created inadvertently at the point of manufacture or subsequently caused by damage /wear and tear / weather conditions). The first author is a UK police officer and, like his senior analyst colleague who is the second author, has wide experience in testing and developing ANPR systems. The authors have been commissioned by the UK Home Office to carry out post graduate ANPR research at the University of Hertfordshire.