OK, so you know that the back of your credit card has a magnetic stripe on the back of it. Did you know that it can store three tracks of data, but only two are actually used for credit card transactions? Did you also know that the third line of data was hoped to be able to contain a digital photograph of the the card owner? (but its damned hard to fit a photo in to that few bits of data).
If so, did you know you can actually see the data encoded on your card?
Over the weekend I stumbled upon a very interesting blog titled "Another Science Experiment" covering the use of finely ground rust dust to see how the data is encoded on to standard credit card magnetic tracks.
I'll let the photo's below do the talking...