Dithered QR Codes

A QR code is really just a way of encoding a few bytes of data in a way that can be easily read froma photo by a smartphone or similar device. They're designed to be very robust to bad focus, bad printing, funny angles, and missing areas. Exactly how they work isn't terribly important, but for the purposes of this page, a QR code is a grid of squares that divide into two parts — the function patterns (which are the bold shapes in the above example) and the data modules (everything else). The function modules are mostly used to let the scanner find the QR code easily, so they have to be very clear and distinct. The data modules are where the actual data is stored, along with some extra header data etc, and since those are only read after the scanner has used the function modules to work out exactly where the QR code is, they can be modified a bit more. This is often used by brands to create QR codes that look a bit distinctive, and while this kind of modification makes them a bit less robust when scanning, but you can generally get away with a fair bit before the codes become unscannable.