Automatic License Plate Recognition (ALPR) on a company car park works like this: a camera with AI analytics detects an approaching vehicle, locates the plate in the frame, reads its number and compares it against a list of authorised vehicles. If the number is on the whitelist, the system automatically opens the barrier or gate, and the entry is logged as an event linked to the video recording. In practice the licence plate acts as a credential in an access control system: the vehicle itself is the pass, with no card, no remote and no stopping at the gatehouse.
Most articles about ALPR stop at barrier automation. In this guide we take a wider view: we show how licence plate recognition on a car park becomes part of the security system of the entire site, integrated with the ICT Protege access control platform and the DW Spectrum VMS.
How ALPR works, step by step
Regardless of the manufacturer, the process runs in four stages:
- Vehicle detection. AI analytics tells a vehicle apart from a pedestrian, an animal or a shadow. The system does not try to read a plate where there is none, which cuts down false events.
- Plate localisation and reading. The algorithm finds the plate in the frame and reads the characters using OCR. Modern deep learning cameras handle both domestic and foreign plates and can read them on a moving vehicle.
- Comparison against a list. The recognised number is checked against a database: a whitelist of authorised vehicles or a blacklist of unwanted ones.
- Decision and event logging. The system opens the gate, raises an alarm or simply records the passage. Every event carries a timestamp, the recognised number and the associated video clip.
In the portfolio of the American manufacturer Digital Watchdog, whose cameras you will find in our CCTV camera catalogue, the AI Deep Learning analytics covers both ALPR and MMC, that is recognition of the vehicle make, model and colour. MMC catches the situation where a different car tries to enter with a whitelisted plate, for example after a plate theft.
Installation requirements: what determines read accuracy
An ALPR camera is not just an ordinary camera pointed at a gate. Reliable reading requires a well thought out installation:
- Mounting angle and height. The plate should be visible as close to head-on as possible, with a small vertical and horizontal angle. Too steep an angle distorts the characters and degrades OCR accuracy.
- Plate size in the frame. The characters need enough pixels for the algorithm to distinguish them. In practice this means matching the focal length to the distance of the read point, rather than using a wide shot of the whole entrance.
- Illumination. At night an IR illuminator matched to the distance is critical. Plates are retroreflective, so poorly chosen lighting can blow them out into a white blob.
- Shutter speed for moving vehicles. A moving vehicle requires a short shutter time, otherwise the characters blur. A dedicated ALPR camera freezes the motion at the cost of a darker scene, which it compensates for with the illuminator.
- One read point per lane. The best results come from a pinch point where vehicles pass one by one along a predictable path, for example just before the barrier.
Vehicle whitelists and blacklists
Lists are the heart of the system. The whitelist holds authorised vehicles: employee cars, the company fleet, regular subcontractors. For them the gate opens automatically. The blacklist works the other way round: a vehicle from that list triggers an alarm for the security team, for example a car linked to a previous theft or a person banned from the site. Vehicles on neither list can be handled neutrally: the system logs the passage and security or reception decides whether to let them in.
The plate as a credential: integration with access control
The real value of ALPR shows up once it is integrated with an access control platform. In the ICT Protege environment, for which we are an official certified distributor, a plate number can be treated like any other credential, just like a card or a PIN. That brings concrete benefits:
- One database of permissions. An employee has a card for the doors and a plate for the gate in the same system. Offboarding is one click that revokes both credentials at once.
- Time-limited permissions. A subcontractor's plate can be valid only on working days during the contract hours, or only on the day of a scheduled delivery.
- One event history. A vehicle entry, a door opening and an alarm zone arming all land in a common log. The audit of "who was on site and when" covers vehicles too.
- Video verification. Thanks to the integration with the DW Spectrum VMS, every entry event has a linked recording. The operator clicks the event and immediately sees the camera footage, with no manual archive searching.
How access control, CCTV and intrusion detection come together into one organism in practice is covered in our guide on integrating access control with CCTV and intrusion alarms.
Three typical deployment scenarios
Employee car park
Employees drive in without stopping, without cards or remotes. The system makes sure vehicles of people who no longer work for the company stay out, and reports show the actual utilisation of parking spaces.
Warehouse loading docks
Carriers' trucks go on the whitelist based on delivery notifications. ALPR records the exact entry and exit time of every vehicle set, which brings order to time window settlements and disputes over demurrage. MMC additionally verifies that the vehicle arriving under a given number matches the expected characteristics.
Announced visitors
Reception enters the guest's plate number when scheduling the visit. On the day of the meeting the gate opens automatically and the permission expires when the visit ends. The guest does not wait at the intercom, and security has a full record of who entered and when.
GDPR in brief
A licence plate number makes it possible to identify a natural person, so it is treated as personal data. In practice this means three obligations: define the purpose of processing (access control and site security), set a data retention period adequate to that purpose instead of keeping the entry history indefinitely, and inform people entering the premises about the monitoring and data processing. Consult the legal basis for employee whitelists with the person responsible for data protection in your organisation.
Hardware: what to look for in an ALPR camera
Choose a camera with on-board analytics, an IR illuminator whose range matches the read point, and a motorised zoom lens that makes it easy to frame the plate precisely. As the only Polish distributor of Digital Watchdog cameras, we offer devices from the American manufacturer that are NDAA/TAA compliant, with AI Deep Learning analytics covering ALPR and MMC, ready to work with the DW Spectrum VMS.
Frequently asked questions
Will an ALPR camera read a plate at night and in the rain?
Yes, provided the installation is done right. The key factors are an IR illuminator matched to the read distance, a short shutter time and a frame in which the plate is large enough. Harsh weather reduces the accuracy of any system, which is why the read point is designed so that vehicles slow down, for example just before the barrier.
How does an ALPR camera differ from a regular CCTV camera?
A general purpose camera is tuned for a bright, smooth scene, so the characters on a moving vehicle blur. An ALPR camera works with a short shutter, IR illumination and a tight frame on the plate, and the on-board analytics reads the number and generates an event instead of just an image.
Can ALPR open a gate without a separate controller?
A camera with a relay output can drive a barrier on its own, but in a corporate environment we recommend integration with an access control platform such as ICT Protege. You then gain central credential management, time-limited permissions and a single event history shared with doors and the alarm system.
Planning ALPR for a company car park or warehouse docks? Contact us: we will help you select Digital Watchdog cameras and design an ICT Protege integration tailored to your site.