This is a trick you can play on anyone whose computer you have access to.
Simply use the PRINT SCREEN button on the keyboard to take an image of their desktop. Make sure no programs are open or minimized on the taskbar.
Next, Copy the desktop image from memory to a paint program such as MSPaint and SAVE AS a bitmap (*.bmp) or a JPEG (*.jpg).
Go to Desktop Properties and change background to the file that you just saved.
You may have to Minimize the taskbar from Taskbar Properties. (START --> SETTINGS)
Active Desktop must be enabled(right click on your desktop) and to DISABLE DESKTOP ICONS for the trick to have maximum effect.