Pinterest button dont show thumbnails

Installed the pinterest code on my site for a few days ago and noticed that most of the posts are not getting the thumbnail. it only gets a “media text”. Screenshot can be found here: https://i.imgur.com/8r6qG.jpg

You can try it yourself here: https://funny-pictures-blog.com/2012/05/23/dexter-vs-games-of-thrones/

does anyone know how i can fix this?

im using the same script i got from the pinterest page here: https://pinterest.com/about/goodies/