Cannot get the thumbs

I installed this plugin on an adult porn blog (NSFW!) whose URL is: http://www.roughstraightmen.com.

I can’t seem to be able to get the thumbs (I assume made from the images in the post) via the widget for the most read posts. The option for thumbs is checked and yet I see no thumbs on the blog. There is only textual hierarchy of most read posts.

Is there a solution for this issue? How to see the thumbnails?

http://wordpress.org/extend/plugins/most-and-least-read-posts-widget/