Unlike the older, one-dimensional barcodes that were designed to be mechanically scanned by a narrow beam of light, a QR code is detected by a two-dimensional digital [[image sensor]] and then digitally analyzed by a programmed processor. The processor locates the three distinctive so-called "finder patterns", (each consisting of three superimposed concentric squares of differing contrast<ref>ISO IEC 18004 §6.3.3.1</ref>) at the upper left, upper right and lower left corners of the QR code image,<ref>{{Cite web |title=ISO/IEC 18004:2024(en) - QR code bar code symbology specification |url=https://www.iso.org/obp/ui/#iso:std:iso-iec:18004:ed-4:v1:en |url-status=live |archive-url=https://web.archive.org/web/20250620035759/https://www.iso.org/obp/ui/#iso:std:iso-iec:18004:ed-4:v1:en |archive-date=20 June 2025 |access-date=22 June 2025 |website=[[International Organization for Standardization]]}}</ref> using a smaller square (or multiple squares) near the fourth corner to normalize the image for size, orientation, and angle of viewing. The small dots throughout the QR code are then converted to binary numbers and validated with an error-correcting algorithm.
