Use snapshots from a camera connected to Homey, and let Platerecognizer do AI based licence plate recognition. For every plate the app detects, a flow will be triggered. The app will also provide vehicle type and region.
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The free Platerecognizer service allows you to upload 2500 images per month. The plate detection usually is ready within 1 to 3 seconds from uploading an image (via an action flowcard).
To make testing your flow easier, a test image is available as global image token. It has license plates of two cars and a motor cycle.
I guess it depends where your camera is looking at. I have a foscam camera pointed at my own driveway, and I configured the motion detection to not trigger on passing traffic (that would not be allowed anyway ). So 80 snapshots per day is enough for me, but I agree it is limited.