Automated license plate readers (ALPRs) are high-speed, computer-controlled camera systems that are typically mounted on street poles, streetlights, highway overpasses, mobile trailers, or attached to police squad cars. ALPRs automatically capture all license plate numbers that come into view, along with the location, date, and time. The data, which includes photographs of the vehicle and sometimes its driver and passengers, is then uploaded to a central server.

Taken in the aggregate, ALPR data can paint an intimate portrait of a driver’s life and even chill First Amendment protected activity. ALPR technology can be used to target drivers who visit sensitive places such as health centers, immigration clinics, gun shops, union halls, protests, or centers of religious worship.

Drivers have no control over whether their vehicle displays a license plate because the government requires all car, truck, and motorcycle drivers to display license plates in public view. So it’s particularly disturbing that automatic license plate readers are used to track and record the movements of millions of ordinary people, even though the overwhelming majority are not connected to a crime.

Threats Posed by ALPR

ALPR is a powerful surveillance technology that can be used to invade the privacy of individuals as well as to violate the rights of entire communities.

In addition to the risk of deliberate misuse, ALPRs sometimes misread plates, leading to dire consequences. In 2009, San Francisco police pulled over Denise Green, an African-American city worker, handcuffed her at gunpoint, forced her to her knees, and searched both her and her vehicle—all because her car was misidentified as stolen due to a license plate reader error. Her experience led the U.S. Ninth Circuit Court of Appeals to rule that technology alone can’t be the basis of such a stop, but that judgment does not apply everywhere, leaving people vulnerable to similar law enforcement errors. 

Aggregate data stored for lengthy periods of time (or indefinitely) becomes more invasive and revealing, and it is susceptible to both misuse and data breach. Sensible retention limits, specific policies about who inside an agency is allowed to access data, and audit and control processes could help minimize these issues. One of the better privacy protections would be for police to retain no information at all when a passing vehicle does not match a hot list. 

This page was adapted from the Street level Surveillance Project of the EFF