Automated License Plate Recognition
Law enforcement agencies throughout the nation and around the world are increasingly adopting Automated License Plate Recognition (ALPR) systems to enhance their enforcement and investigative capabilities, expand their collection of relevant data, and expedite the tedious and time consuming process of comparing vehicle license plates with lists of stolen, wanted, and other vehicles of interest.
This webpage was created to share information, resources, and best practices associated with ALPR policy, planning, implementation, management, and performance.
ALPR systems function to automatically capture an image of the vehicle’s license plate, transform that image into alphanumeric characters using optical character recognition or similar software, compare the plate number acquired to one or more databases of vehicles of interest to law enforcement and other agencies, and to alert the officer when a vehicle of interest has been observed. Learn more about all of the elements of automated license plate recognition, and its use and deployment by law enforcement.
Law enforcement use of automated license plate readers is often reported in local, regional, and national media. News stories reviewing the deployment and use of ALPR help document how this technology is implemented, its value for law enforcement and public safety, and emerging trends in policy and operations.
Additional News Articles
- License Plate Readers a Great Tool for Cops; Privacy Concerns (10/30/16)
- A Look at Plate Readers That Helped Catch Murder Suspect in West Carthage (7/3/16)
- New Law for Automated License Plate Readers (4/22/16)
- License Plate Readers are Used to Fight Crime (1/31/16)
- The NYPD is Tracking Drivers Across the Country Using License Plate Readers (1/27/16)
- How Police Catch Uninsured Drivers (12/23/15)
- Four Suspects in Custody After Plate Reader Alerts Monrovia Officer of Stolen Vehicle (12/11/15)
- LA's Plan to Scan Plates and Send 'Dear John' Letters (12/2/15)
- Driving a Stolen Vehicle to Jail to Pickup Girlfriend (11/30/15)
- License Plate Readers Exposed! (10/28/15)
- More details on VSP use of ALPR in Virginia shooter case (8/28/15)
- ALPR Use by Tennessee Highway Patrol (8/28/15)
- Scanner Effective, Sudbury Police Say (8/28/15)
- ALPR Halting Drug Flow on the Eastern Shore (8/27/15)
- ALPR Technology Picked-up Virginia Shooter's Car (8/26/15)
- Rochester NY: Police License Plate Readers On The Shelf...For Now (8/5/15)
- Novato's Automated License Plate Reader Helps Locate Stolen Cars (7/26/15)
- Louisiana Governor Vetoes LPR Bill, Citing Privacy Concerns (6/20/15)
- Public Safety But At What Cost (5/31/15)
- 8 Ways Police Can Spy on Crime, and You (5/21/15)
- Striking a Balance on Privacy in Virginia (5/9/15)
- Appeals Court Says Police Can Withhold License Plate Scans (5/6/15)
- Link to the ruling: ACLU v. Superior Court of Los Angeles County (5/6/15)
- Chico Police Link 66 Vehicles to Crime with use of ALPR (4/10/15)
- Police Chief Defends ALPR (4/2/15)
- DHS ALPR Solicitation (4/2/15)
- ARS Technica: We Know Where You've Been (3/24/15)
- Joint Letter on ALPR by Law Enforcement Organizations to Congress (3/10/15)
- Vermont Annual Report on ALPR now available
- LA: License plate recognition system helps locate suspect in fatal shooting (3/9/15)
- IL: SB1351 - Automated License Plate Recognition System Data Act (2/18/15)
- IN: Do license plate readers invade privacy? (2/16/15)
- GA: Police use license plate readers to catch suspect accused of robbing Facebook user (2/13/15)
- CA: Alameda police happy with new license plate reading technology (2/10/15)
- MN: State lawmakers debate shelf life of license-plate reader data (1/24/15)
- Rincon Police nab offenders with automatic license plate reader (12/31/14)
- MN: Lawmakers Plan to Limit Police Use of License Plate Data (12/22/14)
- California bill would set rules on license plate readers (12/17/14)
- New license plate reader catches 'most wanted' suspect (12/8/14)
Policy & Privacy
ALPR technology must be properly deployed and carefully managed to ensure effective operations that recognize and respect the privacy interests and the civil rights and civil liberties of citizens.
Owners of motorized vehicles driven on public thoroughfares are required by law to annually register their vehicles with their state bureau or department of motor vehicles, and to attach license plates that are publicly and legibly displayed. Vehicle license plates generally consist of a series of alpha numeric characters that reference the license plate to the specific vehicle registered (including the make, model, year, and vehicle identification number (VIN)) and the registered owner and/or lien holder of the vehicle.
ALPR systems capture a contextual photo of the vehicle, an image of the license plate, the geographic coordinates of where the image was captured, and the date and time of the recording. The ALPR system does not identify any individual or access any person's personal information through its analysis of license plate characters. The data captured by the ALPR unit itself is entirely anonymous. Officers can only identify the registered owner of a vehicle by querying a separate, secure state government database of vehicle license plate records, which is restricted, controlled, and audited. The federal Driver's Privacy Protection Act (DPPA) restricts access and prohibits the release of personal information from state motor vehicle records to ensure the privacy of citizens. 18 USC § 2721-2725.
Many jurisdictions are actively developing or considering legislation that will authorize, limit, and/or restrict the use of ALPR systems and the data they generate. At least 14 states have enacted legislation on the use of ALPRs. More detailed information can be found here.
Policy & Privacy Reports
- DHS: PIA for Acquisition/Use of Commercial Service (4/2/15)
- ARJIS Acceptable Use Policy for the Regional License Plate Reader System (2/13/15)
- IACP ALPR Policy and Operational Guidance
- IACP ALPR Privacy Impact Assessment
- NCRIC Privacy Impact Assessment
- Texas DPS Privacy Impact Assessment (Sep. 2014)
- RCMP Privacy Impact Assessment
- US DOJ - Privacy Impact Assessment Guidance
- DHS/FEMA Privacy Impact Assessment Guidance
- RAND License Plate Readers for Law Enforcement
Research & Reports
Jurisdictions throughout the nation and around the world are continuing research on current operations, emerging best practices, performance metrics, and business benefit realization.
Recent research reports:
- Vermont Department of Public Safety, Annual Report to the Vermont Senate and House Committees on Judiciary and Transportation as required by: 23 V.S.A. S 1607 Automated License Plate Recognition Systems (2015)
- RAND, License Plate Readers for Law Enforcement (2014)
- Roberts & Casanova, IACP ALPR Policy and Operational Guidance for Law Enforcement, (2012)
- Bart Custers, License Plate Readers in the Netherlands, (2012)
- Lum, Merola, Willis, and Cave: License Plate Recognition Technology (LPR): Impact Evaluation and Community Assessment (2010)
- Cohen, Plecas, and McCormick: A Report on the Utility of the Automated License Plate Recognition System in British Columbia (2007)
- Watson and Walsh: The Road Safety Implications of Automatic Number Plate Recognition Technology (ANPR) (2008)
Frequently Asked Questions
How does Automatic License Plate Recognition (ALPR) technology work?
ALPR systems generally consist of a high speed camera with an infrared (“IR”) filter or two cameras—one high resolution digital camera and one IR camera—to capture images of license plates; a processor and application capable of performing sophisticated optical character recognition (OCR) to transform the image of the plate into alphanumeric characters; application software to compare the transformed license plate characters to databases of license plates of interest to law enforcement; and a user interface to display the images captured, the results of the OCR transformation, and an alert capability to notify operators when a plate matching an agency’s “hot list” is observed. The precise configuration of ALPR systems varies depending on the manufacturer of the equipment and the specific operational deployment.
What data does an ALPR system collect?
ALPR systems typically capture the following information: a contextual photo of the vehicle, an image of the license plate, the geographic coordinates of where the image was captured, and the date and time of the recording. The systems also typically identify the specific camera/unit that captured the image. The ALPR camera does not identify any individual or access their personal information through its analysis of license plate numbers. The data captured by the ALPR unit itself is completely anonymous. There is no personally identifiable information contained in an ALPR record and the operator can only determine the registered owner of a vehicle by querying a separate, secure state government database of vehicle license plate records, which is restricted, controlled, and audited. The Federal Driver’s Privacy Protection Act (DPPA) restricts access and prohibits the release of personal information from State motor vehicle records to ensure the privacy of citizens. 18 USC § 2721-2725.
How long are ALPR records retained in a database?
Agencies vary in their ALPR data retention policies based in part on their strategic and tactical objectives in using the technology, and the specific laws and regulations of their jurisdictions. Research is presently underway to define specific ALPR metrics that will help in establishing an empirical foundation to data retention policies.
Who typically has access to an ALPR database? Is there an audit trail?
Only authorized law enforcement personnel who have met the minimum training, certification, and background checks required for access to criminal justice data should have access to the ALPR database. Access to an ALPR database should be restricted to trained and authorized law enforcement users who have a specific and approved authorization to access the database for a lawful purpose that includes both a need to know and a right to know the information. All queries for ALPR data should be subject to auditing and all access should be recorded in audit logs which should be maintained for a suitable period of time consistent with state records archival laws. Audit reports should be structured in a format that is understandable and useful and contain, at a minimum:
- The name and agency of the law enforcement user;
- The date and time of access;
- The specific data accessed;
- The authorized law enforcement or public safety justification for access, including a relevant case number if available.
What are examples of a lawful purpose to access an ALPR system?
Examples of lawful purposes to access an ALPR system may include:
- Locate stolen, wanted, or suspect vehicles
- Locate suspect(s) of criminal investigation or arrest warrants
- Locate witnesses or victims of violent crime
- Locate missing children, elderly persons, or other missing persons (Amber/Silver Alerts)
- Protect the public during special events/situational awareness
- Protect critical infrastructure
How accurate is the ALPR technology?
As ALPR technology is translating optical characters to digital data there is a small error rate in translation of alphanumeric characters that are similar in shape. ALPR operators must recognize that the data collected from the ALPR device, and the content of the referenced "hot lists," consists of data that may or may not be accurate, despite ongoing efforts to maximize the currency and accuracy of such data. To the greatest extent possible, vehicle license plate information must be verified from separate law enforcement information sources to confirm the vehicle's alert status and justification for law enforcement contact. Law enforcement users of ALPR data must, to the fullest extent possible, visually confirm that the plate characters generated by the ALPR readers accurately correspond with the digital image of the license plate in question.
Can I request the images of where my vehicle has been seen by ALPR?
Availability to ALPR data in most jurisdictions is restricted to law enforcement personnel with a lawful purpose to access the data, as well as a need and right to know the information. Access to ALPR data is typically restricted and strictly audited. There are law enforcement agencies that do allow access to ALPR data for the registered owner of the vehicle on a case-by-case basis. Please contact your city, county, or state law enforcement agency for their specific ALPR policies to determine if you have access to ALPR data related to your registered vehicle(s).
Do ALPR systems provide constant surveillance of my location?
No. ALPR systems do not provide constant surveillance of vehicles. The systems do provide authorized law enforcement personnel with a pointer for one moment in time and the location where a vehicle's license plate passed an ALPR device.
Can ALPR devices see into my vehicle and do they use facial recognition software?
Unlike red-light cameras, ALPR devices do not have illumination to aid in identifying the driver or potential passengers of the vehicle. The purpose of ALPR technology is to identify vehicles, not the occupants. If ambient lighting is sufficient or a subject is outside and near the vehicle at the time an ALPR-equipped vehicle passes, their image may be captured in the contextual photo taken by the ALPR unit of the vehicle. This contextual photo is simply designed to provide context, i.e., to identify the specific vehicle to which the license plate is attached to aid the operator in quickly identifying which of several vehicles in the immediate vicinity is carrying the alerted tag. ALPR systems are not designed to collect images of drivers or vehicle occupants, nor are they integrated with facial recognition solutions or any applications that simultaneously identify the registered owner or passengers.
Is every ALPR image reviewed?
No. Images captured by ALPR systems are only reviewed by law enforcement personnel when required for a lawful purpose and all access is strictly monitored and audited.
What federal laws are there regarding the use of ALPR systems?
At the time of this writing there are no federal laws that explicitly govern or limit the use of ALPR technology or taking photographs of things that are plainly visible from public spaces by law enforcement agencies.