Provided og:image is not big enough
facebook-opengraph, facebook-social-plugins, image
Solution
I solved using informations from this and this posts.
You can try using an image that is bigger than 200x200, with dimensions multiple of 100, and squared.
Other useful stuffs are using jpg extension, host the image in the same server of the website and avoid any "strange" chars in filename.
Problem
Since some days I'm experiencing this problem. Here is my debug The image provided is bigger than 200x200 px, it has unique link and there is any redirection on that page. Linter response is 200. When I copy and past page's link on fb it give me the choice between 3 images that are smaller than 200x200px and the one I've provided is ignored. But If I try to share it through "Like button" or "Send button" it works fine. It sounds like a fb Bug. Thx