What is a QR code?
A QR code is a machine-readable code that carries information in a two-dimensional pattern of squares. It can contain text, a web address or other data interpreted by applications. Developed by DENSO WAVE, it encodes information horizontally and vertically, unlike a one-dimensional barcode.
Reading and error correction
Distinctive position patterns at the corners help readers locate the code and determine orientation. The surrounding blank area also matters for reliable reading. Error correction allows recovery under some conditions when part of the code is damaged; it does not tolerate every kind of damage. More data creates a denser pattern that can be difficult to read in small print. Poor contrast, glare, curved surfaces and excessive decoration affect scanning. Codes should be tested with different phones at realistic distances before printing. If a restaurant menu code contains only an address, the menu file is not inside the code; it is downloaded from a server after scanning.
Static, dynamic and safe use
The data in a static code does not change. Solutions described as dynamic generally use a redirect address whose destination can be changed through a service. That convenience also creates dependence on the redirect service. A QR code's appearance does not establish that its destination is trustworthy. Placing another sticker over a printed code can lead users to a fake payment or login page. Users should inspect the domain before opening a link and be cautious about unexpected password or payment requests. If a code contains an access key or personal information, people who can photograph it may also obtain that data. Purpose, data content and destination continuity should be planned together.