How QR codes store data and survive damage

A QR code is a two-dimensional grid of black and white modules that a phone camera can read to recover stored data such as links or text. Its three corner finder patterns let a reader locate and orient the grid, while alignment and timing patterns correct for angle and size. Data is encoded as bits read in a fixed zigzag order, with format information telling the reader how to decode it. Reed-Solomon error correction adds backup data so a code still scans when partly torn or covered, at four levels from L to H. Higher correction levels make codes more robust but hold less data and look denser.