Where are app-provided wallpapers stored? There are some apps on Play Store that provide some wallpapers that can then be set as home background from various launcher, such as Nova, Apex, etc.

Where do these apps store the wallpapers? I looked in the usual locations, such as /data/data/, or /sdcard/Android/data, but I couldn't find anything.

EDIT: Here are the details: Galaxy Nexus, with latest Paranoid Android (which builds on top of Android 4.4.4). The app in question is like all the apps that add wallpapers to use with the most used launchers. I would say the name, but it probably would be considered spam.

I want to extract the wallpapers because I run into a strange issue: when I select the wallpaper with Nova it does not get set and I get all sort of errors in the logcat. The process in charge of setting the wallpaper then keeps retrying and uses all the phone resources. I have to remove the battery out of the phone because it isn't responding. I don't know if the issue is solvable. I searched but hardly anything relevant turns up. So I wanted to inspect the wallpapers and maybe reduce them in resolution, just to see if that worked.
Check out this answer, just in case the wallpaper was moved

That being said, since you're looking for an app-provided wallpaper and not a system provided wallpaper, we'll probably need to know the package name of the application in question (and you'll need to have root access to your device, which I believe you already have). 

So assuming the package name of the app is com.example.superdupperlauncher, then you would need to look into /data/data/com.example.superdupperlauncher/files/ or /data/data/com.example.superdupperlauncher/