Read QR code from photos library

It can't read it from your photos library. Under Settings > Camera you can turn on the option to Scan QR codes. When that is enabled you can point your camera at a QR code and you get the option to read it. You can't just take a picture of the code and have the phone decipher it.

I use this workaround:

I send the QR code via email from my camera roll to my computer or to another mobile device and, on that unit, I make it show on the screen, then I use my iphone to read it.

Regards

Giulio