Read a barcode from a picture

Why a barcode is less forgiving than a QR code

A striped barcode carries no error correction at all. A QR code stores redundant data so that a scratch, a logo printed over the middle or a torn corner still reads; a one-dimensional barcode stores each digit exactly once, in a fixed pattern of bar widths, with nothing spare. So anything obscuring part of the bars — glare on a glossy label, a crease, a curve around a bottle, a tear, a marker pen — means no read rather than a partial one. That is a property of the symbology, not a limitation of this page, and it is why supermarket scanners fire a line of light across the code from several angles at once.

What protects against misreads instead is the check digit. In EAN-13, UPC-A, EAN-8 and ITF-14 the last digit is computed from the others, so a digit read incorrectly makes the whole number fail its own arithmetic. It is verified here and shown to you — which means a number that reads and checks is very likely correct, and one that fails the check is reported rather than handed over looking plausible. Code 128 and Code 39 have their own internal checks.

The picture matters more than for a QR code, for the same reason. The code should be square to the camera, in focus, evenly lit and as large in frame as you can get it, with its quiet zones — the clear margins either side — intact. A photograph taken at an angle skews the bar widths, which is precisely the information being measured. Cropping tight to the bars removes the quiet zone and makes a perfectly good code unreadable.

No product database is consulted, and nothing is looked up. You get the number, the symbology it was encoded in, and whether the check digit passes — not the name of the product. That requires querying a commercial catalogue, which would mean sending your scan somewhere, and the whole point of doing this here is that nothing is sent anywhere.

When you want something else

For scanning things rather than reading pictures of them, a phone camera app is the right tool: it reads continuously, tries many frames a second, and adjusts focus and exposure until one works — which is a far better strategy than a single still photograph. Most phone cameras now do this natively without any app at all.

For looking up what a number means, you need a catalogue. Open Food Facts is free and open for groceries, and GS1's own registry resolves the company prefix in any EAN or UPC, which at least tells you who issued it. For scanning at volume — stock-taking, asset tracking — a dedicated handheld scanner reads a code in a fraction of a second and types the number wherever your cursor is, which no photograph-based approach can match.