This isn't necessarily a new technique, as black and white art has been put on floppies before: https://github.com/bzotto/picturedsk

But the new wrinkle here is support for grayscale, meaning photos or other grayscale artwork can now be put on a disk.

We can even put the art inside of valid sectors to keep the disk appearing completely normal to casual observation from a host computer.

Using the Green channel instead of the Red is much more likely to make a good looking grayscale image.

But how do you hide the floppies?

Just having that media would be suspicious in and of itself...