At NWHacks in 2018 my team and I made a system to digitize player piano music scrolls using openCV. Using a camera, the location of the holes in the piano scroll is detected. The presence of a hole in a particular column corresponds to the press of a key on a piano. Once the location of the notes is known, the data is turned into a MIDI file and can be played back.
A Raspberry Pi 3 and camera are used, which allowed for quick prototyping in the fast-paced hackathon environment.