This involves one simple registry tweak and making or finding a picture.
Open Regedit. You can do this by holding the Windows Key and hitting R, which opens Run. Now type in “regedit” then hit enter.
Double-click on “OEMBackground” and change the value from 0 to 1.
Create a JPEG smaller than 250Kb and save it as “backgroundDefault” in the
C:\Windows\System32\oobe\info\backgroundsfolder. Create the folder if it doesn’t exist yet.
Now, log off or lock your computer to see the changes. Windows Key + L.