Extracting a number plate from a vehicle image
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I am developing an automatic number plate recognition application. I have managed to locate number plate areas by locate rectangular objects in an image. At first I set a minimum height and a width for the number plate of the image so that I could filter the unwanted tiny rectangular bits on the Image. furthermore I use the number plate height and width ratio to filter out false number plates. 

but the issue I have is with the values I set for minimum and maximum number plate height and width, because whenever the distance between the camera and the vehicle change the number plate area will not be recognized.

is there a method to overcome this issue?