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.