Windows 8 will add the ability to let users set a desktop wallpaper as their logon or lock screen as well.
This functionality was some sort of official in Windows 7 but it seems that an option to change Logon screen has been added in Windows 8 Personalization Center. In earlier posted screenshots about Automatic Colorization in Windows 8 Aero, there is a new option in “Desktop Background” section. The checkbox is titled as “Show desktop background images on logon and lock screens”.
This built-in functionality to change Windows 8 Logon Screen will enable users to get rid any tweak or 3rd party tools offering same service.
Credentials: Within Windows and Winsupersite.