I did not know that...
Everyones familiar with Bar Codes, they're read by an ultra violet scanner. If you've ever used the Self Check Out at your local Supermarket, you've used one. They're finicky, sometimes you have to try again, and again to get the scanner to read the code.
Well the solution to that for high speed applications like production lines, where parts are speeding past an eye on an assembly line, is this QR Code, it can be read by visible light sensors, like your camera phone!
FilterBlogs URL in QR Code
QR (Quick Response) code was invented by Denso-Wave Inc. in 1994.
I could imagine 'Secret Agents' embedding information in all kinds of visual media with this technology; like in a photograph in a magazine or even in a video stream!
Bar Code image courtesy Sundeep Mathur's Young Professional/Student Blog (A good article on the history of Bar Codes as well)
I created FilterBlogs QR Code Image with The QR Code Generator application at Kaywa.com
Wikipedia on QR Code
Michael Holloway in QR code