This repo contains simple Python code for controlling a Raspberry Pi along with a webcam, a few relays and colored lights, to scan and validate Digital Green Certificates (EU Digital Covid Certificates).
The relay shield is a Keyestudio KS0212, but any other solution would work, all you would have to change is maybe the GPIO pin assignment according to your custom wiring.
The /etc/rc.local line to run it properly could be something like this:
su pi -c /home/pi/qrcode.py </dev/null >/tmp/qrcode.log 2>&1 &The principle of operation is inspired by the work of lovasoa and gilbsgilbs's tweets on how all this works.
This system does not scan 2D-DOC codes (Datamatrix), mostly because pylibdmtx is incredibly slow and I could not find suitable other implementations for Python on Datamatrix reading.