Quiet zone and contrast
The empty margin around a QR is part of the standard. Cropping it to hug a photo edge is a common reason “nice” designs fail in the wild.
In layouts, treat the quiet zone as a protected box. Do not let logos, stickers or folds invade it.
Contrast under real light
Aim for dark modules on a light field. If brand colours are pale, put the code on a white plate rather than forcing low-contrast modules.
Outdoor posters fade; choose inks and materials that keep dark modules dark after sun exposure.
Patterns and logos
Decorative module shapes and centre marks are fine only while scanners still decode. After styling, test several phone models. If scans fail, reduce decoration before you reduce size.