Lock Screen Reflection is a tiny Windows 10 tool which automatically sets the current lock screen image as your desktop wallpaper.
The program has no graphical interface, and doesn't need to run in the background to do its work. Simply double-click lsr.exe when you need to use it and Lock Screen Reflection updates your wallpaper, then shuts down immediately.
Command line options include setting the wallpaper mode (tiled, stretched etc), saving the image locally, and only saving it (don't see the wallpaper, just save a local copy of the lock screen image).
Lock Screen Reflection provides a basic but effective way to save and reuse the Windows 10 lock screen image.