Here is the first glimpse of Microsoft’s Windows 8 user interface – screen grab of Welcome Screen that lets users login into Windows. The user interfaced design(fonts & current date/time information) is derived from Windows Phone Metro UI and it’s for good (click on the below image for clear view).
Information that is provided in the various blogs suggests that Windows 8 has a built-in customization feature for changing backgrounds of Windows 8 Logon screen ( In earlier versions of Windows we had use third party tools for the customizations)
Via WithInWindows