The FBI claimed they could communicate by changing just a few bits in a graphic. Yeah, right...
Yes, this is very, very possible. A friend of mine at work is a programmer. (I'm a software tester.) I asked him if this was possible, after seeing it in a really bad movie.
Anyway, over lunch, he hacked together a quick and dirty program that does just that. Basically, it changes the colors in a few pixels at the edge of a BMP file. Minor changes, but the end result is that the color value for each of those pixels contains a coded reference to a single ascii character. Considering he did that in about 20 minutes, and I saw it work, I have no doubt that someone could easily, very easily do this given a few days time and an average to good programming skill. Granted, my friend's version only contained up to 255 characters and could only use bitmaps. But given any resonable amount of time, this would be a piece of cake.
LOL, maybe the FBI misspelled it by goofing one letter and it came out as 'bits.'