You may have noticed that some police cruisers have little boxes mounted on the front and back of the car that point outwards. Those are license plate scanners, which automatically read the license plates of the other cars on the road. They allow police officers to check to see if a car is stolen or if there is an APB out on the owner, without having to manually read and type out each plate. License plate scanners are relatively new technology, but Redditor tim_macgyver has built one using a Raspberry Pi.
A license plate scanner needs to do three things: identify if a license plate is in the field of view, scan that license plate, and parse it to determine what the plate number is. That requires computer vision, and for that tim_macgyver is using OpenALPR (Automatic License Plate Recognition). OpenALPR is software designed specifically for building license plate scanners, and it’s open source.
To utilize the OpenALPR SDK, tim_macgyver is running a Node.js service on his Raspberry Pi that automatically takes a photo every second with a camera connected to the Pi. That photo is then processed by OpenALPR to determine if there is a license plate in the frame. If there is, it scans the license plate and returns the plate number. This is a prototype build for one of tim_macgyver’s clients, but you could certainly make one yourself.