A new feature of iTunes 11 has come to light, users can now redeem Apple iTunes Store cards by holding the code up to the FaceTime camera on an iMac computer.
iTunes uses the camera to scan the code (that is underneath the silver scratch panel on the card), and then credits your iTunes Account accordingly.
See also: iTunes 11 Review
Unfortunately the service isn't yet active in the UK, which still just has the text box for users to enter the digits manually. US cards are not vaild for the UK account (and vice versa). But we assume it'll be rolled out to the UK shortly after its been tested in the United States.
To test out the service open iTunes and tap Store. Then click the Redeem button on the left-hand sidebar.