Windows 7 now supports the ability to load images into the background of the login screen without the use of third-party software or manual hacks. Here’s how to turn it on:
First, a check is made to determine if the customization functionality is enabled or not. More precisely, a DWORD value named OEMBackground in the HKLM\Software\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background key is checked. Its data, of Boolean type, defines whether or not this behavior is turned on, i.e. 1 for enabled, 0 for disabled. This value may not exist by default, depending on your system. Afterwards, if customization is enabled, the primary monitor’s screen height and width are retrieved via calls to GetSystemMetrics.