Zerif Lite PLEASE HELP with Image Issue…

Thanks in advance. I really need some wonderful person here to help me figure this out. What I want is a set image to be displayed when my site link is given. For example, when pasting in my link on FB, I would expect to have one image of my choosing displayed. However, what happens is that I paste the link and an image box/slideshow of sorts is displayed where you can scroll through four different images that random from my media library! Whaaaat? Can someone please tell me how I can make a featured image JUST FOR THE SITE ITSELF? Thanks!
http://www.scribalocity.com