Sometimes QR codes are posted online and because they're online, you can't use the phone camera to scan them. A feature to scan the current phone screen for QR codes would be great instead of downloading some risky 3rd party app. Maybe a button in the quick panel/menu to start a scan for qr codes would be a good way of doing it. Ask if you have any questions.
If you swipe down into your quick settings, there should be a button (or option to add) "Scan QR code." This way you can scan the QR codes from screenshots or saved pictures. Do you not see this option? What phone do you have?
