A QR code reader that works from an image seems almost magical, you hand it a picture and it pulls out a link. Understanding roughly how it does this helps you give it the best chance of success and troubleshoot when a read fails.
Step One: Locating the Code
The reader first scans the image for the telltale finder patterns, the three large squares in the corners of every QR code. These act as anchors, letting the software locate the code within the picture and figure out its orientation, even if it's rotated or at an angle.
Step Two: Reading the Modules
Once located, the reader maps the grid of dark and light modules inside the code. It interprets this grid according to the QR standard, translating the pattern back into the stored data, usually a web link.
Step Three: Correcting Errors
QR codes include redundancy, so the reader can fix minor errors from blur, damage, or a centered logo. This is why a slightly imperfect code still reads. Beyond a certain amount of damage, though, recovery fails.
Helping the Reader Succeed
Give it a clear, complete code with visible corners, decent resolution, and a margin around it. Crop out clutter if needed. The cleaner the code, like one made with a good image QR generator, the easier every step becomes.
FAQ
Common questions are answered in the FAQ section below.