When you share a post on Facebook, or when Jetpack Publicize publishes a post to your Facebook page, Facebook crawls the page and looks for Open Graph meta tags in the head to build a complete post preview (with an image, title, description, ...).
Jetpack will add these meta tags for you, except if you already use another plugin to manage Open Graph meta tags on your site.
I notice that you're using the "Add Link to Facebook" plugin. That plugin offers options to control the meta tags, so Jetpack Open Graph meta tags are disabled.
I'm not familiar with that plugin, but you can contact the plugin author if you don't manage to control the image meta tag.