I'll share a trick how to change your logon background via regedit.
Just follow step below :
1. Press windows+R to open run.
2. Type regedit to run registry editor.
3. Enter to this location :
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI\Background
4. Right click OEMBackground and choose modify.
5. Change Value Data to 1 and then OK.
6. If you didn't find OEMBackground, please make a new file with click Edit > New > DWORD (32-bit)Value .
7. After that, go to C:\Windows\System32\oobe than make a new folder here. Give info for the name of this folder. 8. Make a new folder inside info folder with backgrounds name.
9. Than copy a picture will be your logon background to backgrounds folder.
10. Make sure your picture in jpg extencion with backgroundDefault.jpg name and small than 256 KB.
Enjoy your new logon background :).
