How to change windows 7 login background

Follow These steps

Step 1: Hit  regedit command on cmd.

Step 2: Nevigate to

HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Windows/CurrentVersion/Authentication/LogonUI/Background. 

Step 3: Select OEMBackground

            If the key does not exist, add a new DWORD value with the name OEMBackground.

Step 4: Double click on the entry OEMBackground, and change the value from 0 to 1.

Note : on selecting a new theme in the Appearance and Personalization window will “reset” this registry value. to avoid this please do following

 Launch gpedit.msc.

Navigate to the following section in the Group Policy Editor window:

Computer Configuration\Administrative Templates\System\Logon

You’ll see a setting named “Always use custom login background.” Double-click it and set it to Enabled.

Now its time to set image

Note: Image must be less than 256 KB in size.

Windows looks the custom login screen background image in the following directory

C:\Windows\System32\oobe\info\backgrounds

If info and backgrounds folders don’t exist, create it. and copy your image in it  with the name backgroundDefault.jpg.