facebook pic not the features pic of the blog post

i’m having this problem with all my pages: if i post the link to any blogpost page on facebook, the feature picture is not shown but always the “logo” of my site.

since the fb-debugger also shows no solution, i think this logo picture is set on default somewhere – but i don’t know how to change it.

some advice would be much appreciated!

The page I need help with: [log in to see the link]