I suppose there is no wallpaper setting in Computer settings.
User Config\Administrative Templates\Desktop\Active Desktop\Active Desktop
Wallpaper
"Specifies the desktop background (wallpaper) displayed on all users'
desktops. This setting lets you specify the wallpaper on users' desktops and
prevents users from changing the image or its presentation. The wallpaper you
specify can be stored in a bitmap (*.bmp), JPEG (*.jpg), or HTML (*.htm,
*.html) file. To use this setting, type the fully qualified path and name of
the file that stores the wallpaper image. You can type a local path, such as
C:\Windows\web\wallpaper\home.jpg or a UNC path, such as
\\Server\Share\Corp.jpg. If the specified file is not available when the user
logs on, no wallpaper is displayed. Users cannot specify alternative
wallpaper. You can also use this setting to specify that the wallpaper image
be centered, tiled, or stretched. Users cannot change this specification. If
you disable this setting or do not configure it, no wallpaper is displayed.
However, users can select the wallpaper of their choice. Also, see the Allow
only bitmapped wallpaper in the same location, and the Prevent changing
wallpaper setting in User Configuration\Administrative Templates\Control
Panel. Note: You need to enable the Active Desktop to use this setting.
Note: This setting does not apply to Terminal Server sessions."
BR,
Denis