How-to Change logon screen in Windows 7
If you want to change your logon screen background to a image that you like instead of the default one, there are many ways to do that.
one is changing the registry key
HKLM\Software\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background
and setting the OEMBackground key value to 1.
and then creating a folder “info\backgrounds”under %windir%\System32\oobe\
and then placing your image file with a size of 256kb with a file name of backgroundDefault.jpg.
that is too much to do to change my logon image, here is the simple and easiest way.
download this free and simple tool and you are done, you can put any image into your logon screen with few clicks.
http://tweaks.com/software/tweakslogon/
Note: if your image don't match with your screen resolution this tool will adjust it accordingly, so make sure you select a image with required size and quality