Hey there,

I am sorry for the delay of this reply,

It seems like Facebook do not accept those non-sef post URL so they can't retrieve all the correct image from your blog page.

If I temporary switch your site to SEF, then paste this link http://is-natural.com/test/2016-02-04-00-08-02.html to Facebook debugger tool page https://developers.facebook.com/tools/debug/og/object/ , it will recrawl all the correct image again when you share in Facebook.

You can take a look of my screenshot below, it should show correctly for the post image.

By the way, I already help you switch back to use non-sef, what my suggestion is switch to SEF from backend > global configuration .

Hope this help.