[nayuki]

Please don't call these QR codes; they are simply proprietary 2D barcodes (respectively Facebook Messenger and Snapchat).

The Snap code looks like a 18×18 grid of dots with the center punched out. This probably conveys about 200 bits of information. I suppose that could encode 30 ASCII characters which should be enough to describe a unique username. Or maybe it is a random binary number that is an opaque user ID in Snapchat's database. Either way, I'm guessing that the graphics and algorithm are a trade secret, so you can't get a definitive truth on how these barcodes are generated.

The Messenger code seems hard to analyze because of its different bar lengths and circular layout. The four bulls-eye patterns remind me of QR alignment patterns. I have no idea what the information-theoretic capacity is, but I'll guess it's in the order of magnitude of 500 bits. Again, I suspect the algorithm is not available to the public.

As for Spotify Codes, I discussed them in https://www.reddit.com/r/programming/comments/9th8a7/creatin... .