QRCode

[ghost]

Better use a digitally signed pdf and not a image.
An image can later be manipulated.

[ypiguet-epfl]

My understanding is that it's the QR code message itself which is signed ("tamper-proof signed QRCode"), not its visual rendering or PDF container. There is no much gain to stack signatures. The purpose of the QR code is to be scanned in a standard way and only the message data, after error correction, to be used (digital signature checked or validation by some central database).

[ghost]

I think the spec need to be improved to really make sure that no image on a device is arround that could be captured for manipulation.