Earlier quoted context omitted.
Why not just show a QR code on the screen and have the phone scan that. If it's been taking pictures, it can take one more :)
Because almost every single use of QR codes I've seen has been a terrible UX mistake. They're unwieldy, slow and annoying.
Similarly, if you're at a new computer and you want your phone to authenticate that computer, the computer just needs to display a QR code that your phone scans. The phone then authenticates to the service, sends the token in the QR code, and the computer you're at is trusted. Even easier than bumping.