Cemeteries in Munich allow QR codes as memorials on headstones, Mr. Hoerauf said, and for more than a decade, people whose loved ones are buried in cemeteries around the world have uploaded photographs and other digital keepsakes to create online memorials that can be viewed via QR code.

Initially, some thought the QR code mystery may have something to do with Nazi propaganda, partly due to a past incident in 2004

More than 1,000 stickers were put on gravestones and wooden crosses at three cemeteries in the German city, without any indication of where they came from or why. The 1.95 by 1.2-inch stickers are printed with a QR code,