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

• height of the symbols is not less than 15 px, width is not less than 2px;
• 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.