What a QR code is (and how it actually works)
A QR code is a two-dimensional barcode invented by Denso Wave in 1994. Instead of a row of vertical bars, it uses a grid of black-and-white squares called modules — the position of each module encodes bits, and Reed–Solomon error-correction blocks are woven through the grid so the code can still decode even when a portion of it is damaged, dirty, or covered by a logo. The three big squares in the corners are position markers that tell scanners how the code is rotated; the payload is everything else. Modern smartphones detect QR codes directly from the camera preview — no scanner app required.