Chances are, your local or state police departments have photographs of your car in their files, noting where you were driving on a particular day, even if you never did anything wrong.

Using automated scanners, law enforcement agencies across the country have amassed millions of digital records on the location and movement of every vehicle with a license plate, according to a study published Wednesday by the American Civil Liberties Union. Affixed to police cars, bridges or buildings, the scanners capture images of passing or parked vehicles and note their location, uploading that information into police databases. Departments keep the records for weeks or years, sometimes indefinitely.

As the technology becomes cheaper and more ubiquitous, and federal grants focus on aiding local terrorist detection, even small police agencies are able to deploy more sophisticated surveillance systems. While the Supreme Court ruled in 2012 that a judge’s approval is needed to track a car with GPS, networks of plate scanners allow police effectively to track a driver’s location, sometimes several times every day, with few legal restrictions. The ACLU says the scanners assemble what it calls a ‘single, high-resolution image of our lives.’

‘There’s just a fundamental question of whether we’re going to live […]