How to Change the Logon Screen Background in Windows 7 through Group Policy

First, Create a jpg file you want as logon screen background which should be less than 256kb, name it as backgroundDefault.jpg and place it inside a server share, ex. \\servername\share\backgroundDefault.jpg

1. Copy our wallpaper file to the user’s workstation.
2. Instruct Windows to use our file instead of the default %WinDir%\System32\oobe\background.bmp file.

With the  Group Policy Preferences , we can copy our wallpaper to the user’s computer, while reserving the right to pull it off if the computer leaves the scope of the GPO.  To copy files, open GPMC and follow these steps:

In the Group Policy Management Console, edit the GPO to change following settings.
Computer Configuration => Preferences => Windows Settings => Files => New File 

Select Replace

Type in the UNC path for your source file.

     for example:\\servername\share\backgroundDefault.jpg    

     Remember this file needs to be <256K

    Also understand the permissions on this share need to allow the workstation’s computer     account READ. If you leave the usual “Authenticated Users” 

For the Destination File, type this exact text (without the quotes, and no line breaks):

“%windir%\system32\oobe\info\backgrounds\backgrounddefault.jpg”

Click the “Common” tab

Select “Remove this item when it is no longer applied”. This will ensure your file is removed if:

     •The GPO is deleted or disabled

     •The workstation is moved to another OU where the policy is not linked

     •The policy is filtered out

     •You update your policy to send a new wallpaper file

Optionall: Select Item-level targeting to specify only Windows 7 computers. This will ensure your file isn’t sent to versions of Windows that wouldn’t make use of it anyway.

Now we need to instruct Windows to render this image when the login screen is displayed.  If you read the above article, you’ll remember the OEMBackground registry key.  The good news is, we don’t need that key because there is actually a setting to enable it in GPMC already.

In the same Group Policy Object, navigate to:

Computer Configuration\Policies\Administrative Templates\System\Logon.

Once there, select “Always use custom logon background” and set it to “Enabled”.  This has the same effect of setting the registry manually.

now apply the policy, and run gpupdate /force to check whether its working or not.