Getting a QR code from your screen into a picture
A QR code in an email, a PDF or on a web page is a problem for a phone camera, because you would have to point the phone at the screen. A screenshot solves it, and you can paste it straight into this page.
- Windows: press Win+Shift+S, drag over the code, then paste here with Ctrl+V.
- Mac: press Shift+Cmd+Ctrl+4 and drag over the code to copy it, then paste with Cmd+V. Shift+Cmd+4 saves a file instead.
- iPhone and iPad: take a screenshot, then choose it from your photos.
- Android: take a screenshot, or long press the image in your browser and save it, then choose the file.
- A PDF: take a screenshot of the page or part of it, or export the page as an image.
A screenshot of a code on a screen is often cleaner than a photo of it, because there is no glare, blur or angle.
How big a picture needs to be
The scanner needs to tell the squares of the code apart. As a rule of thumb each square should be at least 3 or 4 pixels wide. A small code with 25 by 25 squares therefore needs a picture of at least about 100 pixels across, and a denser code needs more. If the picture is smaller than that, scaling it up first does not add detail, but a sharp screenshot at a higher zoom level does.
There is no upper limit worth worrying about. A 12 megapixel photo from a phone, 4,000 by 3,000 pixels, is first read at up to 3,200 pixels on its long side, which is most of its full size. If no code is found, a second reader tries it at about 1,600 pixels, then at 800, then in four overlapping quarters, and then in small tiles at full size, which helps with a small code in a wide photo. Pictures over 80 MB are refused to protect your browser.
Several codes in one picture
A sheet of stickers, a poster with a code in each corner or a scan of a page of labels holds more than one code. The scanner finds them together, up to 100 in one picture, and outlines each with a number so you can match it to the details below. If it finds 100, it says so, because the picture may hold more. Codes that are very close, overlapping or at the edge of the picture are the ones that get missed. When only the second reader is available it reads one code, hides it and looks again, which works for a few codes and is weaker on a crowded sheet.
If a code is missing from the list, crop the picture so that code fills more of it, and add that crop on its own.