The Square Full of Information
QR codes are everywhere now: on posters, packaging, restaurant tables, and tickets. You point your phone camera at the little square of black and white blocks, and a moment later a website opens or some information appears. It feels almost magical. But a QR code is not magic, and it is not a picture. It is a clever and very deliberate way of storing data in a visual pattern.
A Pattern, Not a Picture
The name QR stands for Quick Response, and that speed is the whole point. A QR code is a type of barcode, but a more advanced one. An old-style barcode stores information in a single row of lines. A QR code stores information across a two-dimensional grid, both left-to-right and top-to-bottom. This grid is made of many small squares, called modules, each one either black or white. That arrangement of black and white squares is the encoded data.
From Squares to Data
Computers handle information as a code of ones and zeros. A QR code turns this idea into something visible: a black square can stand for one value and a white square for the other. So the pattern of squares is really a stored message written in a visual form. When text, such as a web address, is turned into a QR code, special rules convert that text into the specific arrangement of black and white modules you see.
Scanning and Decoding
When you point your phone's camera at a QR code, the camera captures the image of the pattern. Software then reads the grid of squares and translates it back into the original information. QR codes also include certain fixed patterns, such as the large squares in the corners, which help the scanner find the code and figure out its orientation, so it can be read even at an angle. They also carry built-in error correction, which lets them still be read correctly even if part of the code is dirty or damaged.
Source
This article was written using information from Wikipedia.