QR Code Quiet Zone
The quiet zone is the blank white margin required around every QR code — a minimum of 4 modules wide per the official ISO/IEC 18004 specification — that scanners use to detect where the code pattern starts and ends.
It's easy to overlook because it looks like empty space, but the quiet zone isn't optional padding — it's part of how the code works. A scanner's decoding algorithm looks for a sharp white border to locate the code's edges before it even starts reading the pattern inside.
The most common way this breaks in practice: someone crops a QR code image tightly to "clean it up" for a design layout, cutting into or removing the quiet zone entirely. The data pattern is still intact, but a lot of scanners will fail to even recognize there's a code there.