This Utility Can Change Your Windows 10 Login Image
Windows 10: The new version of Windows, oddly enough, does not allow you to change the image that appears on the login screen when you first start your computer. This tiny utility, aptly named Windows 10 Login Background Changer, can do it for you.
The utility is available on Github. After downloading and launching the application, you can choose a specific image or solid color to display on startup before logging in. You can also turn off things like user info or network and shutdown icons in the bottom right corner of the screen. your screen, although it is unclear if this will break any functionality of your machine. However, changing the background image should work fine.
Change the Windows 10 login background | Github via How-To Geek