We use the codes from Facebook, Google+ etc. and therefore don’t have any influence over which text & pic is shared.
Note that you can define an image as “Featured Image” which tells Facebook / Google etc. to take that one. You’ll find this “Featured Image” section in your blog’s admin area where you can edit your blog post, i.e. here.
You can crosscheck which image Facebook will take by entering your URL on https://developers.facebook.com/tools/debug/og/object/.
Still not fixed? We’re happy to look into it as part of our Premium Plugin. If we don’t manage to fix it, you’ll get a full refund.