I Built An (Almost) Decentralized Facial Recognition System With Raspberry Pi Zeros! - Fras
FRAS allows tens of facial-recognition-camera-clients aka tiny Raspberry Pi-es to be deployed all across a campus, which then record who they see and when they see then to a central database.
Show availability status via a Pi 3 and Pi Zero by hosting a Flask service that uses Socket.io to relay updates. Pi's talk to each other via USB/Ethernet.