Steganography
It sounds cool, but why not simply encrypt the wallet file.
An encrypted file looks like an encrypted file, data encrypted in an image, sound file etc... looks like
an image and sound file.
Crossing a border with a SD card full of images, is easier than an SD with one encrypted like file on it.
I could email a bunch of images to myself, or store them online, and no one would every know.
I'd like to remove the need for relying on my USB, I can memorise my key image and encrypted image.