If you ever want to change your login background on Windows, follow these steps.
To Resolve: Edit
1. Run - regedit
2. Navigate to: HKEY_Local_Machine\Software\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background
3. Change "OEMBackgrond" to "1".
4. Now Run - %windir%\system32\oobe.
5. Create a folder called "info" and a subfolder called "backgrounds" if they don't exist.
6. Copy any new wallpaper you want to that directory following these conditions:
a. Must be named "backgroundDefault"
b. Must be ".jpg" extension.
c. Must be less than 256 KB in size.
Download and run the tool at http://www.julien-manici.com/windows_7_logon_background_changer/.