How To Change Logon Screen Background in Windows 7

Type REGEDIT in start menu search box or run and press Enter.
Navigate to the following registry key:
HKEY\LOCAL\MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background
Right-Click on the right-side pane and select New -> DWORD (32-bit) Value.
Type OEMBackground as the DWORD's value name.
Double-Click on the DWORD value called OEMBackground.
Type 1 in the Value Data box and click OK.
Exit the Registry Editor.
Go to:
C:\Windows\System32\oobe\info\backgrounds (Change C to your system drive)
Copy the image which you want to use as the logon screen's background image and paste it there. The image must have to be in JPG format and it's size should not be more than 256 KB.
Rename the image to backgroundDefault.jpg. Now log-off or switch user to see the new background.

Type CMD in start menu search box or run and press Enter.
Type the following in Command Prompt:
TAKEOWN /F %windir%\system32\imageres.dll && ICACLS %windir%\system32\imageres.dll /GRANT Administrator:F
Go to C:\Windows\System32 (Change C to your system drive) and make a backup of imageres.dll.
Download and run Resource Hacker.
Open C:\Windows\System32\imageres.dll in it. (Change C to your system drive)
Click on the Action menu and select Replace other Resource ….
Click Open file with new resource… and browse for the image that you want to use as the background of the logon screen.
Type IMAGE in the Resource Type box.
In the Resource Name box, type the bold characters given below according to your screen resolution:
- 5031 = 1280 x 1024
- 5032 = 1280 x 960
- 5033 = 1024 x 786
- 5034 = 1600 x 1200
- 5035 = 1440 x 900
- 5036 = 1920 x 1200
- 5037 = 1280 x 768
- 5038 = 1360 x 768
- 5039 = 1024 x 1280
- 5040 = 960 x 1280
- 5041 = 900 x 1440
- 5042 = 786 x 1280
- 5043 = 768 x 1360
  If you can't see your resolution here, use the resource with the resolution closest to your resolution.
- Click on Replace.
- Click on the File menu and select Save.
Restart your PC.
Go to C:\Windows\System32 (Change C to your system drive) and delete imageres_original.dll. Now log-off or switch user to see the new background.