Here's my situation:
I had an image from a website which I set as my background inside the browser. I am wondering now where I can find the image in the file system, because I can't find it online anymore. I am rooted.
I'm not sure if it's the same on older systems, but on ICS it appears to save directly to
/data/data/com.android.settings/files/wallpaper. I set mine from the browser, pulled that file, then changed it to a .png extension and viola - it was the image I had set.
It also appears that this file simply gets overwritten when you change your wallpaper, so I don't see a way to recover one once it's changed unless you have a copy of the image somewhere else.
This also appears to be where it's saved on CyanogenMod 7, so it's possible that this is the "standard" location (certainly a good place to check, at least).
I was annoyed by the exact same problem, so I have programmed an app that automatically saves your wallpapers and your live wallpapers too. It makes it easy to revert to a previous wallpaper. It is called Wallpaper Saver, by Appdictive, and it's free in the Play Store. (It does not require root access.)
In Android 7.0, it's located in
/data/system/users/0. You'll have to use a file explorer to rename it to a jpg or whatever it is. The folder also contains your lockscreen wallpaper so that's a plus.
You can Use Root browser, EE file explorer or other root folder browsers for this. Go to the root path using Root browser (or Es file explorer) and then:
When you try to open it, it won't open. To open it:
Copy the images with high size (Maybe more than 80 Kb since they got a quality) and paste them into a folder that is not in a root directory. (Just copy it to your "Downloads" folder or to your SD card)
Rename it. But when you do this, don't forget the ".jpg" at the end of the name you type. E.g. If I rename it to, "Sukkoth.jpg"
Open it using Gallery or any image viewer app.
In android 7.1.2 I found them here but they do not have extension :
and here too as suggested above
Image extension can simply be added to those files.
in Android 9 (my S10+), wallpapers (lock & regular) are stored in:
Internal Storage/Android/data/com.android.systemui under internal storage.