No Pic when posting to facebook

I don´t know what happens, but since today when I am posting as a admin of an facebook-page articles @ facebook, facebook isn´t showing the article-pictures in the posting, what is not good because the activity on the posting is not good. Can you give me a hint, why the pictures of the articles are not shown anymore? (the last weeks it was working)

page: http://www.90minuten.at
article for example: http://www.90minuten.at/index.php/tageb ... a-zu-gehen

I've checked this example page code and see that og:image attribute is not set, please try set image in standard article options, like here >> http://d.pr/i/MDky