Recommended Camera Position
A good ANPR engine can read plates from images captured in various conditions. However, to achieve over 95% recognition rate with short recognition times, the position of the camera have to be calculated accurately. The best position is if the angle between the camera axis and the direction of the vehicle movement is minimal (see below).
The distance between the camera and plate is also important. If the camera is too far from the plate, the characters may not be large enough for recognizing them. In this case, zoom-in until you reach the proper size. If the distance is too short it may happen that, a part of the plate is over the camera’s field of view (when the vehicle is near to the side of the lane or the plate is not at the middle of the vehicle).
Generally, sharp and characters easily readable to the human eye are appropriate for ANPR/LPR purposes. The most important factor is the size of the characters on the image. For Latin characters it is recommended to have at least 16 pixel character height, for Arabic or other special characters it is recommended to have 20 pixel height (since they are more calligraphic than Latin characters). Too large characters are also not suitable for ANPR, therefore try to avoid settings where the character size is greater than 50 pixels in height.
A line width of a character on the image should be at least 2 pixels.