But by encrypting the file, you're tipping me off that there is something unusual about that particular file that warrants attention. And if (when ) I decrypt the file, I'll definately know somethings up when it just turns out to be a picture of your dog, or something equally mundane.

Stego is by it's nature designed to hide stuff right in the open. Back in world war I or II, information used to be stored on microdots, and hidden on a period at the end of the sentence...

All software installed leaves traces, even applications that run from floppy sometimes "hook" into windows api calls and leave traces....

Even though stego detection is still in it's infancy , relativiely speaking, programmers are working hard to find common traits among stego tools, and they eventually will have apps to find it. I was reading an article (sorry, don't remember where) about using a variant of an electron scanner to look at files, and finding holes in it that could contain data. It did so by making sort of a 3-d "map"...hmmm...I'll have to see if I can remember where I read that....