It is immediately suborned by police to verify if you have your car registered correctly or other 'money making' acts.
I was quite surprised to be pulled over by a cop a few years ago and told that my registration was expired. Especially surprising because my car had it's proper stickers and I'd just finished registering it a few weeks prior.
But apparently the local county DMV records that the city PD was using were out of date, so he thought I was using illegal stickers or some crap. So to say that they only use these licence plate readers for catching 'stolen cars' is pretty much a bald faced lie.
They'll use it every which way they can and "catch" all the criminals, damn their privacy.