Picture selection in Facebook when clicking Pay with a Like?

I wonder how the picture which shows up in facebook gets selected by the "Pay with a like" plugin. In my opinion it should be the featured picture of a blog post.

People click like and there shows up a totally different picture. I use the plugin for weddings ... so it is odd when a different couple shows up in facebook ... haha. Example here: http://wedding.freshphotography.com.au/2012/11/rajneeta-nav-indian-pre-wedding-shoot/

Is there a way to select this? Or is my plugin installation clashing with something? Which picture should the plugin select?