Forces the Start screen to use one of the available backgrounds, 1 through 20, and prevents the user from changing it. If this setting is set to zero or not configured, then Start uses the default background, and users can change it. If this setting is set to a nonzero value, then Start uses the specified background, and users cannot change it. If the specified background is not supported, the default background is used.
Windows Settings/
Administrative Templates/
Local Computer Policy -> Computer Configuration -> Administrative Templates -> Control Panel -> Personalization
After changing group policy options, you need to update group policy. If you do not update group policy then settings will not effect. To update it just simply type below command and also sample image is shown.
gpupdate /force
In about command we used "/force" option, this will help up to update policy options forcefully.
