I have several images that I use for composition mode backdrops. I keep them all in a specific folder of my project. It would be nice if Scrivener could pick one of these at random whenever I open composition mode.
Would prefer limiting it to a specific folder or selected images just to avoid it trying to use unsuitable images (a chart about the stages of hypothermia?)
Thank you!
Perhaps have a look at no.2
I don’t any of those work, because Scrivener determines which image is shown, not the OS.
You could write an AutoHotKey-script (or the macOS equivalent) to instruct Scrivener to select a different image from a folder each time it starts up or even when Composition Mode is engaged. Possibly even after a set time.
I think that would be a fun thing to create, actually. 
The easiest way to do this would be to use a randomised desktop background, and then set the Composition Mode backdrop to be transparent.
Then perhaps a randomized slideshow, full screen.
(If you don’t want to affect your desktop.)