You'd have to use your own artwork, obviously :-)
You can also use GPG to create a DES/AES encrypted message. Of course, then you have the issue with conveying the key.
Public key would be better, but with modern keysizes, you'd need decent sized images to be able to hold all the data you'd need. The best thing to use with stego would be video or audio. A small bit of video could hold a lot of information. Again, you'd have to source your own stuff though, because you wouldn't want someone to be able to compare against an original. The internet has made it brain-dead stupidly easy to arrange dead drops and such.
I hope it makes the slime at the NSA stay awake nights, just thinking about what we could be doing right underneath their noses with our cat videos.
One of the good reasons for ubiquitous encryption is to simply swamp the NSA. Cloward-Piven style.
However, it’s tough to get people to use even simple encryption tools (not to mention use them well). Maybe 5% of my friends use GPG.