Really wacky idea - Encrypt the message with another image. Why would anyone want this? To get a secret message without leaking as much metadata as email. Instead of sending a 1 on 1 message to a specific email address, you're publishing it to many potential recipients. I have no clue how useful it would be, but seems like a fun excuse to use wand / imagemagick.
Look at the "Encrypting Image Data" section: http://www.imagemagick.org/Usage/transform/
