QR Code

A QR code is a square pattern made up of black and white dots. Hidden within this pattern is a short piece of information, usually an internet address. A camera photographs the pattern, and software converts it back into letters and numbers. For humans the pattern is unreadable, but for machines it is very simple. The abbreviation QR stands for “Quick Response”. The code was developed in 1994 by the Japanese company Denso Wave, originally for tracking car parts in the factory.

The bridge between paper and the internet

Before the QR code, you had to type internet addresses by hand. That costs time and often goes wrong because a letter gets mistyped. A QR code replaces typing with a swipe of the camera. This makes it possible to connect any printed surface with a digital page: a poster, a package, a sticker on a shop window.

Economically, the code became especially important for payments. In China, billions of payments per year run through codes that customers scan with apps like Alipay or WeChat Pay. The merchant doesn’t need an expensive card reader for this, just a sheet of paper with their code. In Europe, many banks use the same principle for transfers: the code on the invoice automatically fills in the transfer form.

One important point is often overlooked: the code itself costs nothing. No one has to pay license fees, because Denso Wave released the technology for free. That’s exactly what explains why it became the global standard rather than a competing format.

What’s hidden in the dot pattern

Each small dot in the grid represents a bit, that is, a yes-or-no decision. Black means one, white means zero. From many such bits, the software assembles letters, similar to how Morse code builds words from dots and dashes. A large QR code can hold around 4,300 characters, roughly equivalent to two pages of a book. In practice, though, usually only a short address is stored, because smaller codes are easier to scan.

The three thick squares in the corners are not decoration. They tell the camera where the code begins and how it is oriented. That’s why scanning also works at an angle or upside down. A fourth, smaller square helps compensate for distortion, for example on a curved bottle.

Particularly useful is the built-in error correction. Part of the dots store redundant data, which can be used to reconstruct damaged areas. Depending on the setting, a code remains readable even if up to 30 percent of its surface is missing or dirty. This is exactly what advertising agencies exploit when they place a company logo in the middle of the code.

From restaurant menus to attempted fraud

Most commonly, QR codes are encountered in everyday life on tickets and menus. Railways use them to check tickets, cinemas use them for entry, restaurants use them to replace the printed menu. Setting up two-factor logins also runs through a code: an app on the phone scans it and thereby takes over a secret key.

But there is a downside that regularly appears in the news. Because nobody can tell just by looking at a code where it leads, fraudsters stick their own codes over genuine ones. On parking meters, the fake code then leads to a fraudulent payment page. Experts call this quishing, a made-up word combining QR and phishing, meaning the theft of login credentials. The best protection is simple: before tapping, check which address the phone displays.

The QR code is often confused with the classic barcode found on groceries. The barcode stores information in only one direction and can barely hold more than an item number. The QR code uses both dimensions of the surface and therefore stores many times more. However, neither is encryption: the content is openly readable by any scanner.