Windows 7 Logon Background Changer is a free open source software that let you change the wallpaper of the Windows 7 logon screen (also known as "welcome screen", "login screen" or LogonUI).

It works with Windows 7 Home Basic, Home Premium, Professional, Ultimate, Enterprise and Starter, in x86 or x64 (32 or 64 bits). It also works on Windows Server 2008 R2 (but you are not supposed to customize a server).