For recognition it is necessary to make sure that frames with number plates fulfill the following characteristics:

• the camera should be installed permanently (for detailed installation information, see the vendor documentation);
• the symbols height for IP cameras should be not less than 20-30 px, for analog cameras - not less than 14-20 px, the stroke width should be not less than 2 px;
• minimum allowed contrast with evenly dirty number plate should not be less than 10% ) contrast differentiation of symbols to the background is 25 on 256 point scale);
• maximum allowed uneven dirtiness is not more than 12% (ratio of the dirty area of the number plate to its whole area);
• geometrical proportions of the number plate picture should not differ from such proportions of the number plate itself with more than 10%.

Basic characteristics of used video cameras are presented in the General requirements for mounting and configuring of cameras section.

Examples of LP images that will be recognized correctly and completely:

To ensure the correct recognition of the LP number, its image should not be:

• unequally lit;
  
• overexposed;
  
• blurred (due to incorrect shutter speed settings for the speed of the vehicle);
  
• distorted (due to incorrect placement of the camera);
  
• interlaced;
  
• dirty.