Open your registry and find the key below.
Modify the value of 'Wallpaper' to equal the path and filename of the bitmap (BMP) file you want to use as the background (e.g. 'c:\windows\mylogo.bmp').
Restart Windows for the changes to take effect.
Note: In the same key, you should also be aware of, and possibly set these additional values "Pattern"="(None)" & "TileWallpaper"="0"
Key:[HKEY_USERS\.DEFAULT\Control Panel\Desktop]
Value Name: Wallpaper
Data Type: REG_SZ
