Why this reads an uploaded image instead of requiring a camera#
The most common real situation is already having an image with a QR code in it — a screenshot someone sent, a saved photo, a poster captured earlier — rather than standing in front of the actual code with a camera ready. This tool decodes directly from whatever image file you already have, which covers that case that a camera-only scanner cannot: there is no code physically in front of you anymore, just a picture of one.
How image-based decoding actually works#
A QR code encodes data as a specific pattern of black and white squares, along with fixed positioning markers in three of its four corners that let a decoder figure out the code's orientation and boundaries even if the photo is at an angle. This tool draws the uploaded image onto a canvas, reads its raw pixel data, and runs a decoding algorithm that locates those markers and extracts the encoded bits — the same fundamental process a phone's camera-based scanner uses, just applied to a static image instead of a live video frame.
What can make a QR code fail to decode#
A QR code with too little contrast, a blurry or heavily compressed photo, or one photographed at too sharp an angle can lose enough of its positioning markers or data cells that decoding fails — this is a property of the image quality, not something this tool can work around. If a scan fails, a clearer, more direct photo of the code (or a cleaner screenshot) is the actual fix.