I know there's probably a gui app but this has it's uses too. It's quick once setup and can be automated easily.
Get some needed packages,
sudo apt-get install zbar-tools
sudo apt-get install xclip
Command to scan a QR and put on clipboard, ready to paste,
zbarimg -q --raw "$1" |xclip -selection c
Command to scan using webcam and put on clipboard - this one puts up a preview and when the green square is good press "space", and close window (X). (Better if it auto-closed...)
zbarcam --raw |xclip -selection c
I put these together into a tiny script that does both depending on file parm given,
if [ -n "$1" ]; then
zbarimg -q --raw "$1" |xclip -selection c
else
zbarcam --raw |xclip -selection c
fi
Now you can attach this script to a menu item, or key or desktop shortcut easily.
For capturing a file you can attach it to a Nautilus Action file selected file as parm (%f) and it will allow you to right click any image to convert. I'd suggest adding a couple mime-type selectors so it only shows for png and jpeg files, not all of them.