For a long time Windows has enabled users to set their own desktop background images. However, a user's ability to change the logon screen image has been pretty much restricted. With the introduction of Windows 7, though, there is a way to customise the start-up picture on the logon screen. It's a little circuitous, but it's fairly simple if you're familiar with navigating your computer.
Boot up your computer. Once it has fully booted up, click on the start menu. Click on the search icon and enter regedit into the search field. Search for the term.
Double click on the regedit icon that appears to access the Registry Editor.
Click on the HKEY_LOCAL_MACHINE icon. Then navigate to Software, then Microsoft, then WindowsCurrentVersion, then AuthenticationLogon, then UIBackground.
Create a new DWORD in the registry and call it OEMBackground. Set its value to one.
Exit the registry. Navigate to the windir folder, then to system32oobeinfobackgrounds. Copy your background image to this folder. Make sure that your image is a JPG file.
Rename your image backgroundDefault.jpg.