A QR code is just a series of square pixels, and whether the pixel is black or white contributes to the data. This has two QR codes, essentially overlayed one on the other. Some pixels are half black/half white, so depending on the angle you hold your phone at, the software that decodes QR codes will detect a different color as being centered in the pixel it's examining. So, based on the angle you hold your phone (some people had better success with rotation), you get one QR code or the other.
What is half black/white though? I don’t see any gray. Only black and white
Did he subdivide the qr code cell into four sub pixels and make the left two one color and the right two another? That’s what I would have guessed for the “lenticular” effect at different angles. But the subpixels I see are more checkerboard ish
QR code decoders usually work by sampling the values from a dot grid overlayed on the camera image (or something along those lines). If a QR square isn’t actually uniform, the sampled value for that square will change if you move the camera a bit. When you hold a QR code in front of the camera, the picture is continuously sampled, yielding different bit values all the time because you don’t hold the camera a 100% still (in addition to sensor noise and the like). The QR decoder is however satisfied as soon as the result passes the QR checksum verification.
The image recognition that outputs the bit pattern of the QR code is inherently heuristic in nature, and only the checksum verification is what decides if the recognition worked successfully. The trick in TFA is to produce an image where two different results of the heuristics can both pass the checksum verification, so which one you get depends on circumstantial factors.
