Steganography that I'm used to seeing intertwined ones data with the actual image data. Which is much more difficult to detect (though certainly not undetectable).
If you're interested why I was playing with all this, it was for storing public keys in gravatar images: http://kybernetikos.github.io/VisualSecrecy/
I wonder answers about "When and why?" questions. Can you guys answer it?
steghide has a far superior approach:
But that can be broken too: