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Detecting vehicles without license plate

Watcher can detect vehicles without license plates. This function is a part of automatic number plate recognition (ANPR) module.

Since recognizing vehicles without license plates requires more VRAM than simple ANPR, this feature is disabled by default. Please refer to Calculating video memory for analytics for details on the resources consumption.

Camera requirements for detecting vehicles without license plates are slightly different from the requirements for recognizing license plates due to the module features.

The main recommendations are as follows:

  • The license plate must be clearly visible throughout the area of interest.
  • There should be no foreign objects (wires, road signs, trees, etc.) that can cover the number in the camera field of view.
  • The vehicle in the camera field of view should move in one direction, i.e. there should be no turns on the road.
  • License plate illumination is required for night and dark operation conditions.


If only some part(s) of the frame comply with the above conditions, you can set the detection zone when configuring ANPR so that the troubled areas were excluded from recognition process.

Below are examples of correct and incorrect installation of cameras.

Frame example Description
✅ Correct installation example
❌ Poor installation example: the license plate is closed by a wire, the license plates are too small
❌ Example of poor installation for night conditions: the license plate is fully flared. The vehicle will be detected, but the license plate will not be recognized, although its presence or absence cannot be confirmed. Additional illumination is required.

Enabling the detection of vehicles without license plates

To enable detection of vehicles without license plates:

  1. Install and configure the ANPR module.


    If a certain lane is not completely visible in the field of view, make sure to adjust the detection area so as to exclude this lane from recognition. Otherwise, all vehicles in the partially visible lane will be detected as vehicles without license plates because the detector will detect the car but will not detect the license plate.

  2. Open the /etc/flussonic/flussonic.conf file on the recognizing streamer to add ssd_net_path /opt/flussonic/lib/vision/priv/ssd_wcar; option in the plugin vision section:

    plugin vision {
        ssd_net_path /opt/flussonic/lib/vision/priv/ssd_wcar;
  3. After saving the configuration file, run the command to apply the changes:

    service flussonic restart

Browsing and searching for vehicles without license plates

The detected vehicles without license plates are included in the general list on the Events -> License plates tab without value in the Plate number column.

Vehicle without LP in the list

To search for events of vehicle without a license plate recognition, you can use an API request like GET http://WATCHER-IP/vsaas/api/v2/analytics/license_plates with the event_type=no_license_plate parameter.


curl -v GET -H 'x-vsaas-api-key: 7c75da8fb314183f1f825271898a3687' \
-d 'limit=12&offset=12&event_type=no_license_plate' \
-H "Content-Type: application/x-www-form-urlencoded;charset=UTF-8" \ 

Put your own API key to the x-vsaas-api-key parameter or use another way to authorize the API request.