When Peter Wayner wrote a book on the practice of steganography in 1996, the term seemed so arcane, so daunting, that his publisher insisted he not use that word in the title.

That changed in the days after Sept. 11, however. Among the many rumors floating around after the attacks, one held that Osama Bin Laden's minions communicated with one another via messages embedded in digital photographs that they sent around the Internet. Or something along those lines. The story was never verified, Wayner says, although the idea brought to light the little-known and ancient art of steganography. As luck would have it, Wayner was updating Disappearing Cryptography (the 1996 version was subtitled Being and Nothingness on the Net) at the time.

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