When a code will not decode, the scanner is rarely the problem. Usually print, size or capture is. This order helps you find the cause systematically.
The seven usual suspects
First, contrast: a light code on a light background fails. Second, size: below 1.5 cm edge length camera scans struggle. Third, quiet zone: without the four-module border the decoder cannot find the structure. Fourth, glare on laminated codes or codes behind glass. Fifth, blur from motion or too short a distance.
Sixth, damage: tears, scratches and pasted-over areas. Seventh, format: some apps only read QR, not Data Matrix or Aztec. Our scan tests every supported format at once — if it fails here, print is usually the cause.
What you can do in 30 seconds
Use screen magnification or camera zoom instead of moving closer. Rotate the image 90 degrees. Photograph the code straight on, not at an angle. Add a second, side light instead of frontal light to kill reflections. For screenshots, crop tighter.
For printed labels: a second print with a larger module size solves more problems than any software change. If you generate the code yourself, consider the error correction level — higher levels consume area but forgive more damage.
When nothing helps
Then the code was probably generated incorrectly. Test it on a second device and a second scanner. If there are still zero hits, regenerate it — with automatically generated database codes, truncated content is the most common cause.
FAQ
Frequently asked questions
Why does my phone fail while another one works?
Camera resolution, focus behaviour and supported formats differ. A browser scanner with multi-format support is often more tolerant.
Does a brighter screen help?
Yes, but avoid reflections. Matte paper beats glossy film in practically every case.
Can a damaged QR code still be readable?
Up to a point, depending on error correction. Practical tolerance ends around 30% destruction.