This video does a nice job explaining how ALPR (Automated License Plate Reader) systems work, and how they can help law enforcement efforts.
The video outlines the obvious benefits of these license plate reader systems, with a dramatic enactment of a child found via an amber alert notification with a license plate tag snagged by the systems multiple cameras, alerting the officer in the vehicle to investigate.
It also outlines how these systems can be used in criminal investigations, such as a burglary case. If there is a license plate or a partial license plate thought to be owned a burglary suspect, the system can data mine for that license plate, and pull up the dates, times, and locations on a map that the plate has been spotted in the past, from any plate scanner that contributes to this database. If the car has been seen in the same neighborhood, they can learn something about where this alleged burglar does his business.
But to have this data assembled means they have to gather massive amounts of location data on absolutely everybody. And they can use this data for, well, who knows? There are no current legal restrictions on accessing this data. If the police want to pull your plate and see where your car has been when tagged by one of these cameras, they can easily do it.
And that should concern anyone who thinks about civil liberties, and doesn’t think the government should be keeping surveillance data on it’s citizens without any cause.