There are quite a few free tools to change the Windows 7 Logon screen like Windows 7 Logon Screen, Account Screen Editor, and Logon Screen Rotator. Login Changer is another useful and free tool to change the Windows 7 Logon. Another good feature of this tool is that you can add a collection of pictures and change between them at a specified interval. You can also reset to default Windows 7 Logon any time.
You can either select a single image or multiple images. In case the image size is large than what is require the tool will automatically resize and save it for you.
Image formats supported by this tool are Bitmap (BMP), Portable Network Graphics (PNG), Joint Photographic Experts Group (JPG), and Graphics Interchange Format (GIF).
The application require .Net Framework 3.5 and works with Windows 7.