QR Code
QR Code
[A smartphone. On the display, the following text:] "To continue installing, scan this code. 12 seconds remaining" [A particularly recursive QR code is displayed on the screen.] [Caption below the panel:] How to freak out a mobile app user.

QR codes (quick response codes) are a type of 2D barcode that can be scanned using any of several apps on a smartphone. This comic illustrates installation of a new application that requires the smartphone to scan a QR code on its own screen. There is no conceivable purpose for such a step, so it would be completely silly. Even with two mirrors or a front-facing camera and mirror, most smartphones would be unable to simultaneously display the camera feed for the QR scanner and the QR code itself. The only way to do it would be to take a picture of the QR code with a digital camera and then scan the screen of the camera. The "12 seconds remaining" part indicates that there is a time limit for this, and thus a quick response is necessary.
If scanned, the QR code in the comic reads http://xkcd.com/1237/scan/ , a link to a nearly identical image, but the line above the QR code reads, "To continue reading," and the caption reads, "How to trap a webcomic reader in an infinite loop". The QR code is identical to the previous one. So, if scanned again, it would simply return the scanner to the same image in an "infinite loop".
[A smartphone. On the display, the following text:] "To continue installing, scan this code. 12 seconds remaining" [A particularly recursive QR code is displayed on the screen.] [Caption below the panel:] How to freak out a mobile app user.
