A QR code scanner turns the square pattern back into the text it stores, usually a web link, but also Wi-Fi details, contact cards, phone numbers or plain text. This scanner reads codes in two ways: from an image (a screenshot, a photo or a picture someone sent you) or live through your phone or laptop camera.
Image scanning tries the picture at several sizes, rotated, with boosted contrast and in overlapping sections, so it can find small, tilted or slightly blurry codes in larger photos. Camera scanning uses the rear camera on phones and stops as soon as it reads a code. Links are never opened automatically: you see the full address, the website name and warnings for common tricks such as link shorteners, bare IP addresses, look-alike characters and unencrypted pages, and you decide whether to open it.
Limits: it reads one QR code per scan (the first it finds). It doesn't read other barcode types such as EAN or Code 128. Very damaged, tiny or heavily distorted codes may not be readable; cropping closer usually helps. A scan that finds no code is normally handed back, so it doesn't use up your free run.