Examples of problems encountered in reading a code

QR Codes can be read reliably when those following the QR Code standards are clearly printed. Therefore QR Codes not following the standards and indistinct ones may not be read with particular kinds of scanners and mobiles phones.
A code that looks like a QR Code but does not follow the standards cannot be called a QR Code.

Examples of QR Codes that may cause a problem in reading operation are to be described.

QR Code whose modules are distorted

When a QR Code is enlarged or made smaller using an image processing tool or the like, every module becomes distorted.
It may look like a normal QR Code, but it may be difficult or impossible to read the code.

QR Code with letters and pictures around it

If letters or pictures are placed around a QR Code, the required margin cannot be secured.
This kind of code is difficult or impossible to read.

QR Code with overlaid letters and pictures

If you place letters or pictures on an area overlapping a QR Code, the contrast between the bright and dark areas becomes indistinct.
This kind of code is difficult or impossible to read.