Change the Logon Screen Wallpaper

1. Open your registry and find the key below.
2. 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').
3. In the same key, you can also modify these additional values "Pattern" and "TileWallpaper" to set the background pattern and Tile mode respectively.
4. Restart Windows for the changes to take effect.

Registry Settings

System Key: [HKEY_USERS\.DEFAULT\Control Panel\Desktop]
Value Name: Wallpaper, TitleWallpaper
Data Type: REG_SZ (String Value)