ALPRs are constantly scanning and recording the images of cars, trucks, vans, and any vehicles that pass into their cameras’ field of view. Once a vehicle comes into an ALPR camera’s frame, the camera automatically captures the visible license plate number, converting the image into alphanumeric data. For every image an ALPR camera captures, the system also records the corresponding date, time, and location.

These ALPR images and their corresponding alphanumeric tags are then automatically uploaded to a central database that may be queried by law enforcement and compared to any outstanding “hotlists” of license plate numbers law enforcement has flagged as a person or vehicle of interest in a criminal investigation. Once an ALPR system spots a match or “hit” from an officer query or a hotlist, it alerts law enforcement agencies that uploaded or subscribe to the hotlist. These matches or “hits” are used by police to stop vehicles during routine patrols.

By analyzing the data of multiple ALPR cameras in aggregate, police can learn information that a single ALPR camera could not reveal alone. For example, if a car travels down a highway that has been outfitted with staggered ALPR cameras, police can determine the real-time location of a vehicle, its approximate speed, and which exit the vehicle uses to leave the freeway. Municipal authorities sometimes use ALPR to track every vehicle that enters or exits a city.

Mobile ALPR cameras attached to police cars allow officers to make vehicle and driver identifications in real-time based on car registration information.  Police may target particular neighborhoods for surveillance by systematically patrolling neighborhoods.

Law enforcement may search these databases for a license plate, a partial license plate, or the make and model of a vehicle to reveal travel patterns of a particular driver. They may also enter an address to identify visitors to the location or enter multiple locations to determine vehicles traveling between them. Police can also reveal associations between vehicles that are repeatedly seen in the vicinity of each other.

Law enforcement agencies generally set their own ALPR data retention policies, maintaining the data for as little as three months to as long as five years, although private vendors who sell ALPR data to law enforcement hold the data indefinitely.

Even if an agency does not own its own ALPR hardware, it may nonetheless access ALPR data collected by another agency or data collected by a commercial provider, such as Vigilant Solutions. 

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The largest sellers of ALPR technology are Vigilant Solutions and ELSAG. ALPR data is collected by a multitude of contractors that are hired by two major companies—Digital Recognition Network (a subsidiary of Vigilant Solutions) and MVTrac. After obtaining the data, companies then share it with law enforcement agencies, and also with private companies, like banks, credit reporting agencies, and insurance companies.

Private companies, unlike government agencies, have far fewer laws that restrict their collection, storage, and use of ALPR data. And private companies are not subject to the same transparency laws that journalists, civil liberties organizations, and members of the public use to learn more about how law enforcement uses ALPR data.

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Where ALPRs Are Used

ALPRs are commonly used throughout the United States by both local and federal law enforcement agencies. In 2013, the ACLU wrote about a 2012 study by the Police Executive Research Forum that showed that 85 percent of law enforcement agencies plan to acquire or expand use of license plate readers by 2017. EFF and MuckRock are in the process of compiling a list of roughly 1,000 agencies known to use Vigilant Solutions’ ALPR technology.

In 2015, EFF obtained data on ALPR use by the Oakland Police Department through a California Records Act request. After analyzing eight days of ALPR use, EFF created a video showing that the Oakland Police Dept disproportionately deployed ALPR technology against poor, communities of color, while leaving more affluent, whiter neighborhoods virtually untouched.

EFF is pursuing separate litigation in Los Angeles to obtain similar ALPR data from the Los Angeles Police Department and the Los Angeles County Sheriff’s Office.

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