They're vulnarable to manual override. With all the techies around, it won't be safe to use due to slight vulnerability that may lead to random hostility.
Or ED-209 is a little too enthusiastic about Bitcoin adoption.....
Robocoin: USD Payment accepted, please show your QR code to the camera to receive your Bitcoins.
(customer fumbles for QR code)
ED-209: Robocoin has asked you for your QR code... you have 15 seconds to comply. (canons ready)