Before editing your windows registry file, it is recommended to make a backup of the registry file.
Step 1: Click Start and type regedit in the search field
Step 2: Right click and Run as administrator
Step 4: Type OEMBackground in the search field and click Find next
Step 5: Double click on OEMBackground and change the data value from 0 to 1
Step 6: Close the registry editor
Step 7: Now go to the path: C:\Windows\System32\oobe
(My windows is in C drive, in your case, it may be different, e.g. if your windows is in D drive, go to D:\Windows\System32\oobe)
Step 8: Create a new folder, name it info and open it.
Step 9: Create another folder named backgrounds
(Now you are here: C:\Windows\System32\oobe\info\backgrounds)
Step 10: Rename your desired image as backgroundDefault.jpg and place it inside the folder backgrounds.
Note: The image size must be less than 245kB.
Step 11. Now restart your PC.