If you like your desktop background wallpaper and don't want anybody to change it then this tutotrial will be useful for you. The tutorial consists of two steps:  

1. Removing the Desktop Background option from the Personalize appearance and sounds screen.  
2. Disabling the Set as Desktop Background option which appears on right-clicking an image.

But before doing that you shud set your favourite wallpaper on desktop.

1.Removing the Desktop Background option

• Click on the Start button
• Type gpedit.msc in the search box and hit Enter. This will open Local Group Policy Editor.
• In the left pane, navigate to User Configuration>>Administrative Templates>>Control Panel>>Display.
• In the right pane, double-click on Prevent changing wallpaper.

•  In the dialog box that appears, click on Enabled and then OK but don't close GPEditor.

 2. Disabling the Set as Desktop Background option

• In the left pane of the local group policy editor, navigate to User Configuration>>Administrative Templates>>Desktop>>Desktop

• Moving into the right pane, double-click on Desktop Wallpaper.
• Click on Enabled radio button.
• In the Wallpaper Name field, type the full path of the wallpaper you want to display.
• In the Wallpaper Style field, select whether you want the wallpaper to be in Center, Stretch, or Tile style.
• Click OK and exit the Local Group Policy Editor.
• Reboot your system to reflect the changes.

Nice one ...keep it up Dishant