Windows 7 Logon Background Changer is a free software that you can use to select 
from a list of images on your computer as logon screen backgrounds. The software works with both RTM and release candidate versions of Windows 7. Here is what you can do with the software:
Select a directory of images from your computer and the images will be automatically resized. They can be displayed either full page or cut to your custom size.
You can flip through the images to select one that will be displayed. No system files are changed by the software which means it’s pretty safe to use.
Windows 7 Logon Background Changer is developed using WPF (Windows Presentation Foundation) which means it requires decent graphics memory and processing to display 3D animations.