What do the 3 squares on a QR code mean?

The three large squares in the corners of a QR code are finder patterns — they tell the scanner where the code is and which way up it sits. Because there are exactly three (top-left, top-right, bottom-left), the camera can instantly work out the code's orientation and read it at any angle, even upside down or mirrored on glass.

The smaller square floating near the fourth corner is an alignment pattern, which helps the reader correct for tilt and curvature (think codes on bottles). The dotted lines connecting the finder squares are timing patterns that establish the grid spacing.

Design tip: logos and colors are fine, but keep those three corner squares and the quiet border zone intact — cover them and the code stops scanning.