License Plate Reader Glossary

A camera system that photographs passing vehicles, uses software to convert the license plate in each image into text, and stores it with the date, time and location in a searchable database. Also called LPR or ANPR.

Source: California State Auditor, Automated License Plate Readers: To Better Protect Individuals’ Privacy, Law Enforcement Must Increase Its Safeguards for the Data It Collects, Report 2019-118 · February 2020 · See: How Flock cameras work

Fixed cameras are mounted on stationary objects such as light poles. Mobile cameras are mounted on police vehicles.

Source: California State Auditor, Automated License Plate Readers: To Better Protect Individuals’ Privacy, Law Enforcement Must Increase Its Safeguards for the Data It Collects, Report 2019-118 · February 2020

The software step that reads the characters on a plate from an image and turns them into text. Errors at this step cause misreads.

See: Misreads and accuracy

Flock's names for features that recognize vehicle characteristics such as make, color and body type, letting users search for a vehicle without a full plate. Vendor-specific terms.

Source: Flock Safety, “License Plate Readers (LPR) Cameras” product page, Accessed 2026-11-05

A company that makes ALPR cameras and software used by law enforcement agencies and other customers. One of several ALPR vendors. Flock Camera Defense is not affiliated with Flock Safety.

Source: Flock Safety, “License Plate Readers (LPR) Cameras” product page, Accessed 2026-11-05

The record created each time a camera reads a plate: the image, the plate text, a time stamp and the camera location. For Flock, it also includes vehicle characteristics.

Source: Flock Safety, “How Flock Protects” (data privacy and trust page), Accessed 2026-11-05 · See: What data ALPR cameras collect

A list of license plates for vehicles of interest, such as stolen vehicles or vehicles linked to investigations. Plate reads are automatically compared against it. Entries can come from national or state databases or be added by an agency.

Source: California State Auditor, Automated License Plate Readers: To Better Protect Individuals’ Privacy, Law Enforcement Must Increase Its Safeguards for the Data It Collects, Report 2019-118 · February 2020 · See: Hotlists and alerts

A notice generated when a plate read matches a hotlist entry. A hit means two strings of characters matched. It isn't a confirmed identification of a vehicle or a person.

Source: Knoxville Police Department, General Order No. 4.26, “Automatic License Plate Readers”, Effective June 27, 2013 · revised July 28, 2026 · ¶¶ 4–5, 10, 15–20, 27 · See: A match is not a confirmation

The FBI's National Crime Information Center, a national database of records entered by law enforcement agencies, including stolen vehicles and stolen plates. ALPR hotlists can include NCIC records.

Source: FBI CJIS, NCIC 2000 Operating Manual, Introduction (excerpts published by Texas DPS), Intro. §§ 1.2–1.3 · edition date not stated in excerpt

Checking with the agency that entered a database record that it is still valid before acting on a hit. The NCIC manual states that a hit alone is not probable cause to arrest.

Source: FBI CJIS, NCIC 2000 Operating Manual, Introduction (excerpts published by Texas DPS), Intro. §§ 1.2–1.3 · edition date not stated in excerpt

The agency that entered a record into a database such as NCIC. Under the NCIC manual, it is responsible for the record's accuracy, timeliness and completeness.

Source: FBI CJIS, NCIC 2000 Operating Manual, Introduction (excerpts published by Texas DPS), Intro. §§ 1.2–1.3 · edition date not stated in excerpt

A plate read that the software got wrong, such as an 8 read as a B. One audit defines it as a read that initially registers as a hit but is a false positive.

Source: Seattle Office of Inspector General, Surveillance Technology Usage Review: Automated License Plate Reader – Patrol (2021 and 2022), September 29, 2023 · pp. 5, 7, 13 · See: Misreads and accuracy

An alert for a vehicle that shouldn't have been flagged. It can come from a misread, an outdated or wrong hotlist entry, or a match on the same characters from a different state.

See: Outdated and incorrect entries

How long ALPR data is kept before deletion. Set by the customer agency and sometimes by state law. In August 2026, Flock lowered its recommended default from 30 days to seven; agencies with an approved period kept it.

Source: Police1, “Flock Safety sets 7-day default for ALPR data, adds mandatory misuse safeguards”, August 14, 2026 · See: How long data is kept

A Flock feature, announced in August 2026, that lets investigators preserve specific ALPR records connected to an active investigation beyond the normal retention period.

Source: Police1, “Flock Safety sets 7-day default for ALPR data, adds mandatory misuse safeguards”, August 14, 2026

A record of who searched stored ALPR data, when, and for what stated reason. Flock says every search is tied to a specific user and logged.

Source: Flock Safety, “How Flock Protects” (data privacy and trust page), Accessed 2026-11-05

A case or report number entered to justify a search of ALPR data. Flock announced it will require one for every law enforcement search by the end of 2026, with emergency searches flagged for review.

Source: Police1, “Flock Safety sets 7-day default for ALPR data, adds mandatory misuse safeguards”, August 14, 2026

The standard that allows police to briefly stop someone: specific and articulable facts suggesting criminal activity may be afoot. It is less than probable cause.

Source: Terry v. Ohio, 392 U.S. 1 (1968) · See: Traffic stops based on an ALPR alert

A fair probability, considering the totality of the circumstances, that a crime was committed or that evidence will be found. Generally required for arrests and search warrants.

Source: Illinois v. Gates, 462 U.S. 213 (1983)

The standard of proof in a criminal case. Due process requires the prosecution to prove every fact necessary to constitute the crime charged to this standard.

Source: In re Winship, 397 U.S. 358 (1970) · See: Vehicle vs. driver identification

The rule that evidence obtained in violation of the Fourth Amendment generally can't be used against a defendant in a criminal trial, including in state courts. Courts recognize exceptions.

Source: Mapp v. Ohio, 367 U.S. 643 (1961) · See: Exceptions to the exclusionary rule

An exception to the exclusionary rule for evidence obtained by officers who reasonably relied on a warrant later found invalid, and in later cases on certain database records or binding appellate precedent. It does not apply where, for example, a warrant affidavit contained knowingly or recklessly false statements.

Source: United States v. Leon, 468 U.S. 897 (1984) · See: Good faith explained

The doctrine that evidence derived from an unconstitutional search or seizure can be excluded along with the evidence found directly. The test is whether the evidence was obtained by exploiting the illegality, not merely whether it would have been found but for it.

Source: Wong Sun v. United States, 371 U.S. 471 (1963) · See: Fruit of the poisonous tree explained

An exception allowing evidence to be used when its connection to a constitutional violation is too remote. Courts weigh the time between the violation and the discovery, any intervening circumstances, and the purpose and flagrancy of the misconduct.

Source: Brown v. Illinois, 422 U.S. 590 (1975) · See: Attenuation and Utah v. Strieff

A request asking a court to exclude evidence from trial, usually because it was obtained unlawfully. Rules and deadlines vary by jurisdiction.

See: Motions to suppress ALPR evidence

The idea that combining many individually public observations, such as a vehicle's movements over time, can reveal enough to amount to a Fourth Amendment search. Reflected in concurring opinions in United States v. Jones, which said longer-term GPS monitoring impinges on expectations of privacy; the Jones majority decided the case on other grounds.

Source: United States v. Jones, 565 U.S. 400 (2012) · See: The mosaic theory explained

The pretrial process for obtaining evidence from the other side in a case. What the defense can obtain, and how, depends on the jurisdiction's rules.

See: Questions to ask your attorney