MassPrivateI has a roundup of links on the topic that you may want to read. The article begins:
Law enforcement agencies throughout the nation are increasingly adopting automated license plate recognition (ALPR) technologies, which function to automatically capture an image of the vehicle’s license plate, transform that image into alphanumeric characters, compare the plate number acquired to one or more databases of vehicles of interest, and alert the officer when a vehicle of interest has been observed, all within a matter of seconds.(spying on citizens & tracking our every movement)
Read more here.