1. Open Run(ΓΏ +R)
2. Go to following path
HKEY_USERS\.DEFAULT\Control Panel\Desktop
3. Create a new string key named “Wallpaper”.
4. Double click on it. It’ll open Edit String Window.
5. Type the path of the image that you want to set as logon screen at Value Data text box.
6. Close Registry Edit.
7. Now restart your computer.