Georgia Tech researchers have developed a tool called Collage that will allow Internet dissidents to insert hidden messages into Twitter posts and Flickr images in order to circumvent the censorship measures imposed by oppressive governments.
The details of this technique (which you can find in Georgia Tech’s netops website) contain some detailed thinking about how to do practical steganography (the art of hiding data in innocuous-looking files). But I can’t help but note that Flickr and Twitter are actually two of the most commonly blocked sites in countries with repressive regimes…