Huge blank images on posts? Are these posts covers? How can they be disabled?

https://www.christcenteredgamer.com/index.php/staff-blogs/entry/learn-to-program-with-small-basic-an-introduction-to-programming-with-games-art-science-and-math

I have tried setting the first image as a post cover but there is still a huge image on top. How can I get rid of this?

On another note when I try to share on Facebook it errors out.