The first thing you need to do is find the background picture you want to use for your logon screen. For this to work your image must be less than 245kb in size and in a .jpg format.
Step 1: Open the Windows Start menu and enter regedit into the search bar.
Step 2: You want to go to: \HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background
Step 3: Once there look for OEMBackground if you don’t find it right-click then New – DWORD (32 Bit) Value name it OEMBackground
Step 4: Double click on the entry OEMBackground, and change the value from 0 to 1.
Step 6: Create a new folder named info, and open it.
Step 7: Create a new folder within info named backgrounds.
Step 8: Copy the background image you want into backgrounds and name it backgroundDefault.jpg
Step 9: Enjoy!
If you would like to follow a video to do the manual Windows 7 logon change than here is a video I made that goes through the same steps and is easy to follow!
If you are uncomfortable with manually tinkering with the registry — or simply have better things to be doing with your time — we understand. Various third-party applications can change Windows 7’s default logon wallpaper, but our personal favorite is Tweak.com’s Logon Changer.
The software is ridiculously easy to use, doesn’t require installation, and it even has built-in tools to automatically resize and recompress your images while leaving the original file untouched. The Logon Changer also lets you quickly change your logon wallpaper back to the Windows 7 default.