Currently, a small image is displayed in the og:image meta tag. This prevents Facebook from displaying their largest feature image size when XFMG media are shared on the social network. I have changed my templates to reference the full-size image URL, as it is for the twitter:image:src Twitter card meta tag. Additionally, if there is no image description defined, Facebook's crawler will grab the following bit of text to display in the news feed, which is kind of awkward. It would probably be better to include a default og:description if the user hasn't entered one on their photo.