Smallvoid.com

Windows 7 no longer supports the classic logon screen, that is available in WinXP. Windows 7 provides a welcome screen, where one can select between the available user accounts.

Windows Vista already provided several options to configure the logon screen, and Windows 7 adds some extra on top.

Change logon screen background

Save the custom background image as backgroundDefault.jpg in the following folder (Must be less than 256 KByte in size):

%windir%\system32\oobe\info\backgrounds

Then activate loading of OEM background image with this DWORD registry key:

[HKEY_LOCAL_MACHINE \Software \Microsoft \Windows \CurrentVersion \Authentication \LogonUI \Background]
OEMBackground = 1

Credits WithInWindows.com