With this process you will learn how to change the Windows 7 Logon Screen without using any third-party software. It’s a very easy way, but you must follow the next steps very carefully, if you don’t want to harm your computer.
First step: Customizing the registry
On Windows Start menu, run the regedit.exe into the search bar.
The registry editor will popup. Search in the HKEY_LOCAL_MACHINE for the OEMBackground registry key, using the find command (Ctrl+f).
As you see above, you will find it in ComputerHKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionAuthenticationLogonUIBackground path. If the key does not exist, add a new dword value with the name OEMBackground. Change the value of this key from 0 to 1 by double clicking on it.
Second step: Changing the logon image
Open Windows explorer and go to path: C:/Windows/System32/oobe or %windir%/system32/oobe.
Create a new folder called info and another one, inside info, called backgrounds.
Place your desired image file in this folder and rename it as backgroundDefault.jpg (images must be less than 245KB in size).