The problem — a logo-in-the-middle QR that scans on your phone and fails on a customer's. What error correction actually is. Levels L (7%), M (15%), Q (25%), H (30%): how much of the code can be destroyed before the data is unrecoverable. Why a logo is "damage". The decoder doesn't know it's a logo. Cover 22% at level M and you are past the budget with nothing left for a scratch, a fold, or bad light. The rule of thumb: keep the logo under 20% of the code's area, and use level H whenever you cover anything at all. Show the same payload at L and H side by side — H is visibly denser, and that density is the redundancy. The three things that break a code faster than a logo: too little quiet zone, low contrast (light-on-dark, or a colour whose luminance is too close to the background), and printing it smaller than 2cm. Link to your own /qr-logo page as the worked example, not as a pitch. “I build FreeOnlineQR , a free QR and barcode generator — the logo tool above is part of it.”