ANPR/LPR Camera Placement: The Complete CCTV Guide

Automatic number-plate recognition (ANPR) and licence-plate recognition (LPR) place unique demands on camera placement. Unlike general surveillance where Detection or Observation is sufficient, a plate-read camera must resolve a small, highly detailed target (a number plate) on a moving vehicle — at a specific point in the lane, often in fractions of a second. This guide covers the four design parameters that determine whether your ANPR camera reads plates or just captures blurs.

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1. Pixel density on the plate

For reliable automatic reading, a number plate must occupy roughly 250 px/m at the capture point — the same density as the Identification DORI tier. Below this threshold, optical character recognition (OCR) engines fail to distinguish characters reliably, especially on dirty, damaged, or non-standard plates.

Required PD(plate) ≈ 250 px/m · plate_width_metres

Example: a UK plate is 0.52 m wide. At 250 px/m the plate spans 130 pixels horizontally — the minimum for most OCR engines.

2. Approach angle

The angle between the vehicle's direction of travel and the camera's optical axis is the approach angle. Keep it under 30° for front and rear plates. Beyond 30°, plate distortion and glare reduce read rates sharply.

Angle	Read rate (typical)	Recommendation
0–15°	> 98 %	Ideal — direct front/rear view
15–30°	90–98 %	Acceptable with good lighting
30–45°	60–85 %	Marginal — expect misses at speed
> 45°	< 50 %	Unreliable — reposition camera

3. Shutter speed and motion blur

At 60 km/h a vehicle moves 16.7 m/s. A 1/250 s shutter captures 67 mm of motion blur — more than a licence-plate character width. For ANPR, use shutter speeds of 1/1000 s or faster.

Motion blur (mm) = vehicle_speed (m/s) / shutter_speed (1/s) × 1000

Example: 60 km/h = 16.7 m/s. At 1/1000 s: blur = 16.7 / 1000 × 1000 = 16.7 mm — under one character width.

4. Lane geometry and capture zone

Position the camera so the plate is readable for at least 2–3 frames (60–100 ms at 25 fps). A 10 m capture zone at 60 km/h gives 0.6 seconds of readable plate — roughly 15 frames. This requires:

Camera height: 5–7 m above lane level, aimed down 10–15°
Distance to capture point: 10–25 m from the camera
Vertical offset: camera above the lane centreline for symmetrical capture of both front and rear plates

Design your ANPR layout in 5 minutes. The free CCTV Design Tool includes a dedicated vehicle simulation module: draw lanes, set approach angles, and release live traffic. Every vehicle is scored in real time for plate-read quality.

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