The immediate issue that you will notice is that the wallpaper displays the same image on both screens.
Here’s how to do it.
We’re going to chooseHeart Broken by Pincel3d, but he’s got some other wonderful wallpapers over there.
Now this next part is slightly tricky if you aren’t familiar.
Note: resized the image down so you’ve got the option to easily see it.
The wallpaper will magically cover that window.
And that’s all there is to it.
You now have two seperate wallpapers!
(or even three)