Automatic License Plate Recognition (ALPR)

Overview#

Detectives investigating a series of commercial burglaries know the suspect uses a specific vehicle. Rather than manually reviewing hours of camera footage, they add the plate to a watchlist. The next time that vehicle passes any camera in the network, an alert fires immediately, with the exact time, GPS coordinates, and a confidence score attached. The investigation has a location lead within minutes of the detection.

The ALPR module manages automatic license plate recognition read records from camera systems and provides vehicle watchlist administration. Every plate detection is stored with confidence scoring, GPS coordinates, and optional watchlist matching. Organizations can conduct targeted vehicle tracking with full audit logging to satisfy chain-of-custody requirements.

Key Features#

Plate Read Records: Capture and store detected license plates with confidence scores, GPS coordinates, timestamps, vehicle type, and vehicle colour from camera systems.
Watchlist Matching: Automatically match detected plates against configured vehicle watchlists for real-time alerts on vehicles of interest.
Vehicle Watchlist Management: Create and manage vehicle watchlists with different list types, descriptions, and optional expiration dates using create-or-update semantics.
Audit Logging: All watchlist modifications are automatically logged through the Operations Log service with user identity, operation type, and metadata.
Row-Level Access Control: Queries are filtered by organisation and access control policies to ensure data isolation and security.
Soft Deletes: Watchlists are deactivated rather than permanently deleted, preserving historical records for compliance and audit purposes.
Paginated Queries: Plate read queries support pagination with configurable limits for efficient data retrieval.
Programmable API Access: Full API support for querying plate reads, managing watchlists, and filtering by plate number.

Use Cases#

Law enforcement investigators add suspect vehicles to watchlists during active investigations, receiving immediate notification when those vehicles appear anywhere in the camera network, reducing the time between detection and response.

Border control agencies monitor specific vehicle plates crossing checkpoints, automatically flagging vehicles associated with smuggling networks, stolen asset investigations, or outstanding warrants.

Critical infrastructure security teams track vehicle movements around protected sites, with watchlist alerts providing early warning when previously identified threat vehicles approach restricted areas.

Traffic and transport authorities analyse plate read patterns across camera networks to understand vehicle movement flows, identify unusual routes, and support post-incident reconstruction.

Integration#

The ALPR module integrates with other Argus modules:

Operations Log: All watchlist mutations are automatically recorded in the operations log for audit compliance.
Alert Management: Watchlist matches can trigger alerts for real-time notification of detected vehicles of interest.
Case Management: Plate read data and watchlist matches can be linked to investigation cases as evidence.
Command Center: Live plate detection feeds and watchlist hit notifications display in the operational command centre.

Open Standards#

GraphQL (June 2018 specification): All plate read queries, watchlist queries, and watchlist mutations are exposed via a typed GraphQL API, enabling strongly typed, self-describing access for integrating systems.
ISO 3166-1 alpha-2: The plate_country field on every read record uses two-letter country codes (for example, "JM" for Jamaica) to identify the national jurisdiction of the detected plate.
WGS 84 / EPSG:4326: GPS coordinates attached to each plate read are stored as decimal-degree latitude and longitude values referenced to the WGS 84 datum, ensuring interoperability with mapping and GIS systems.
ONVIF Profile S / RTSP (RFC 7826): Camera systems that feed plate read records into the module connect via ONVIF Profile S device management and RTSP video streaming, the dominant open standards for IP surveillance cameras.
JSON Web Token (RFC 7519) and JWKS (RFC 7517): Every GraphQL request is authenticated by verifying an RS256-signed JWT against a JWKS endpoint, enforcing strong cryptographic identity assurance on all access to plate data.
OAuth 2.0 (RFC 6749): The Bearer token authorisation framework governs how access tokens are issued and presented, with the JWT carrying the scoped claims evaluated by the permission layer.
ISO 8601: All timestamps, detection time, watchlist creation, and audit log entries, are serialised as ISO 8601 datetime values, ensuring unambiguous time representation across jurisdictions for chain-of-custody purposes.

Last Reviewed: 2026-02-24 Last Updated: 2026-04-14