Common QR code detection problems

An important note to make before looking into why a scanner might not recognise a QR code is that styled QR codes are primarily aimed at users with mobile devices, and those devices employ much more advanced detection algorithms than the embedded or industrial QR code scanners. Therefore, even a highly-customised QR code will work fine for its intended purpose as long as it has sufficient contrast and error correction level to be recognised by a phone camera.

If the customised QR codes are intended to be used with devices such as ticketing machines or other embedded industrial scanners, always verify that the target device can still recognise such code.

Corner dots and squares

They serve as the anchor points for a reader to detect the code. Using simpler shapes and higher contrast for corners can significantly improve code detection, while keeping the rest of the code fully customisable.

Contrast, size and spacing

Avoid light colours on a light background, and dark colours on a dark background. Image plays a role as well; a bold logo with strong colours in the centre of the code requires an equally bold contrast between light and dark portions of the QR code. Always leave some space between the code and any surrounding graphics, e.g. borders, and don't make the code too small (and therefore dense) for the individual dots to be correctly recognised.

Error correction level

A higher error correction level allows the reader to recognise the code even when portions of the code are obstructed or poorly detected from the image. However, it also affects how much data a QR code can fit and how dense it appears.