Attached Link: http://www.flash.net/~bob001/echelon.htm

Yeppers, evildoers have been known to use this technique. They even featured it on "The Agency," so you know it's hot. Actually, there are several algorithms that can detect content embedded within an image. Just as Google and Digimarc have web crawling bots. I'd be fairly sure that the CIA and NSA are on the lookout for these. In fact NSA may not even rely on something so primitive. They have Project Echelon which listens in on (according to reports), virtually every satellite, microwave, fax, telex, cellular, cable and fiber optic communication in the world. They don't need to crawl the web, they grab it off the wire or out of the air. Just to be on the safe side, I wouldn't make my identifying text something like, "release the anthrax tonight."

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken