I have recently moved my last remaining Windows workstation to Windows 7.  The login screen now has a background image that I am not particularly fond of.  It turns out that this relatively trivial to change.

First, click on the Windows buttons (where the old start bar used to be), in the "Search programs and files" box, type regedit.  You should see regedit.exe displayed.  Right click this and select "Run as Administrator (you don't actually use Windows as an administrative user I hope).  Once you type in your admin credentials you see the old trusty registry editor interface.  Find the following registry key:

HKLM\Software\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background

In the right hand side change the value of OEMBackground to 1.

You now need to create two directories in the %windir%\System32\oobe folder, the first called info, and then inside of that one called backgrounds.  Your complete path should look like this:

%windir%\System32\oobe\info\backgrounds

Change the filename of your background image to be backgroundDefault.jpg.  You can also specify different backgrounds for different resolutions, so a filename of background1920×1200.jpg would be displayed when your desktop resolution is set to 1920x1200.  If there is no file for a specific resolution, the backgroundDefault.jpg image will be stretched to fit the current resolution.  Also note that if you have a dual or multi head setup (more than one monitor), the resolution refers to the primary display as it is the only one used during the login process.

In the next week or so I plan to write a powershell script to automate this process.

Kudos go to the site where I first read about this:

http://www.blogsdna.com/2698/you-can-customize-windows-7-logon-background-officially.htm