To restrict users from changing the wallpaper (under your Administrator account), click on Start > Run > type gpedit.msc and press enter.
Next, go to Local Computer Policy > User Configuration > Administrative Templates > Desktop.
In the right pane, select Desktop wallpaper and enable it.
Indicate the full path for your custom/default wallpaper. Center and stretch the image as required and press the OK button to validate.
Now, restart your PC to check the results.
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