You may have recognized the out-of-focus blur in images when you take photos with an open aperture. This effect is called bokeh. Some people at the MIT Medialab use this for a really intriguing concept: Bokode. At first it looks like a LED transmitting just a red light, but by putting the LED out of focus you see, that this light contains information.

This bokeh-code or Bokode is a barcode design with a simple lenslet over the pattern. We show that an off-the-shelf camera can capture Bokode features of 2.5 microns from a distance of over 4 meters

Especially noteworthy is the simple idea how to measure distance and angle just by analysing how many and what barcodes you see. You will find more information at the webpage of the project