Restrict users from changing the wallpaper in Windows

Navigate to the following registry key: HKEY_CURRENT_USER\Software\Microsoft\Windows\ CurrentVersion\Policies\System
Create a new string value called "Wallpaper" and set it to the full path and filename of the image.
Additionally, to specify the display style, create a new string value called "WallpaperStyle" and set it to either "0", "1" or "2" according to the list below.

• 0 - Centered (Default)
• 1 - Tiled
• 2 - Stretched

NOTE: You may need to restart Windows for the changes to take effect.
Original Source: https://support.microsoft.com/en-us/help/555429