How do you keep the QR from looking dirty or old?

The QR is printed clean, with a white margin around the code, so the camera can read it among food photos that do not get in the way. It is replaced when a stain enters the code. Check the codes in the night light, away from splashes on the table. In Madrid the code is stained and the table ends up looking at the photo the floor shows on their camera. Each table has a QR that opens the photo menu, and a clean spare is ready.