Correction adds redundant codewords; the quiet zone separates the symbol from surrounding content. Both improve decoding conditions, but neither certifies a real print or screen.
Higher correction costs capacity
L, M, Q and H trade payload capacity for recovery evidence. A longer payload can require a larger QR version or fail at a high level; QRMaker reports that failure instead of truncating.
The quiet zone is part of the artifact
Every preview and download reserves four light modules around the matrix. Cropping that margin or placing graphics over it can reduce scanner recognition.
Final scanning is still required
Print size, surface, glare, damage, colour, camera focus and surrounding design are outside a browser generator. Test representative devices after the code reaches its final medium.