how to change theme using command prompt

Question

I am working on a desktop app that provide users multiple themes. My requirement is when user click on a theme that should be applied on the desktop. I am using a command line found from here How do I change the current Windows theme programmatically?. But its not working it opens a window that is

and nothing happens.

Also how to add a thumbnail image like in windows personalize Window...

I mean how to show a theme in this way so that all image can be visible on one another