A question I had carried since LumiCode; could the data live in the picture's own grain, with no frame, no finder squares, nothing added on top?
Posterising a photo locks in which pixels are bright, but which exact pixels carry the brightness is free, and that freedom is the whole channel. A phone camera is still hostile territory though: glare, angle, rotation, compression.
Two tiers of one format. DitherGlyph packs dense payloads into the dither arrangement at high resolution, about 0.3 bits per pixel through a PNG; pure, deep at roughly sixteen times the capacity, and sealed with encryption. DitherCode trades resolution for distance; fixed-rate chunky cells and a cat's-eye finder a phone locks onto almost instantly.
Both live: ditherglyph.quiettools.dev and ditherglyph-lite.quiettools.dev. 65 to 105 KB rides in a 2 MP picture; the scannable tier is verified on a real phone at up to 4,665 characters, and its cat's-eye finder worked well enough that I retrofitted it across the LumiCode formats.