HOW TO CHANGE YOUR WINDOWS LOG ON SCREEN

--Open the registry editor by command regedit.

--Go to the key:HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Authentication\ LogonUI\Background

--Double-click the OEMBackground DWORD key

--Set value of the key to 1

--Select a background image for logon screen with size less than 256 KB.

--Copy that image into the C:\Windows\system32\oobe\info\backgrounds folder

--Rename the image to backgroundDefault.jpg. Reboot, and now your logon image would have changed.