"Steganography is the practice of concealing a file, message, image, or video within another file, message, image, or video." (Wikipedia)
IPiggyback manipulates the pixel values of a live stream (from Soho/New York) in real time to encode a layer of information.
Encoding a message into pixel x:30 y:30.
Visitors of the site/project can find and decode that information (140 character messages) as well as choose any pixel and hide messages for others to see. A pixel of choice will be forever changed to carry the message encoded in its colour values.
Decoding the message from pixel x:30 y:30 and replying on x:123 y:111.
With time, the image will be more and more distorted, yet heavier and heavier with information it conveys.
The website my or may not still be up on ipiggyback.leoneckert.com
And the code can be found right here.