- On your computer, open regedit. (proceed at your own risk...)
- Find the following key: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background
- In there look for a value named: OEMBackground and set the value to 1. (It may or may not be there, if it isn't just create a new DWORD value with that name and set a value of 1.) Close regedit.
- Browse to the following path in your Windows directory: %windir%\system32\oobe\info\backgrounds (note: you may need to create the 'info' and 'backgrounds' directories)
- Drop in your desired image file and name it: backgroundDefault.jpg (NOTE: the file size must be less than 256Kb for it to be used)
- Now hit CTRL-ALT-DEL or WIN-L and you should see your new background!