Re: Using a QR code image...
Yes, the idea (as I understand it) is that a QR code is displayed at the till. This will probably be some kind of UID representing the individual transaction.
The app will scan this QR, connect to the service over the internet, and authorise the retailer to pull money from their account for that transaction.
I have to agree that I would worry about fraud. The bank won't take responsibility, as you have authorised CurrentC to take money from your bank account. Just as with Paypal, you would have to take the matter up with CurrentC and/or the retailer if a fraudulent transaction were to take place.