Print and scanning

Readability depends on payload density, error correction, media, lighting, distance, and the scanner. There is no universal minimum size that works for every code.

• Keep at least four empty modules around the code. Frames sit outside that quiet zone.
• Prefer dark modules on a light, matte background. Avoid low contrast and busy photographs behind transparent exports.
• iOS Camera, Android Camera, and dedicated QR apps do not behave identically for Wi-Fi, SMS, geo, and vCard.
• A software decode of the PNG is useful evidence, not a field test. Test a print on the phones you care about.
• Do not encode expiring signed storage URLs. When the signature dies, the printed code dies with it.