Sorry for looting a dead body, but...
It's interesting to find out, that I am not the only one with this wish to sync my wallpapers for all monitors simultaneously by their filenames.
I'd love to read that this "issue" had been resolved in the meantime.
My setup includes 3 monitors with each different resolutions and orientations.
(1.: 2560x1440, landscape,
2.: 1920x1200, landscape,
3.: 1080x1920, portrait)
So I went to collect wallpapers with a really high resolution from which I cut out 3 different parts for each monitor in their native resolution.
I saved them in 3 different directories, naming them (1).jpg, (2).jpg, and so on and set each monitor to their specific directory.
I had worked it out myself by checking "Show in alphabetical order" and setting all monitors to the same amount of time for changing their WPs (like Keith mentioned here).
In 3 of 4 transistions all works fine.
But from time to time, DF fails to change one wallpaper.
(monitor 1 + 2 both show (4).jpg from their specific directories but monitor 3 still shows its (3).jpg)
It is not always the same image failing but I guess it could be the same monitor, but I am not sure.
That would be an EIZO CS2420 (1920x1200) which differs from the other monitors by its color depth. It's got 10 bit instead of 8 bit. Maybe that's the problem?
Since this bothers me a bit, I went to set it back to one image pool and employed Photoshop to compose a huge fixed image (5560x1920) with a transparent background from all of the three specific images.
That works but it's a bit time consuming (if you want more that two different wallpapers).
I hope you guys have a solution or a nicer workaround in mind?
Cheers!
Edit:
According to this thread
https://www.displayfusion.com/Discussions/View/pairing-images-for-multiple-monitors-with-different-resolutions/?ID=7ac0c742-fda1-4bba-8a1b-d79c1029f417
I could try this out to keep my wallpapers paired.
Will keep you up-to-date