Due to the differences with regards to what options different sites need, we decided not to include any OpenGraph/Twitter metadata by default. Instead, we recommend that you choose one of the many plugins which offer this functionality and set the image manually instead of relying on FB / LinkedIn / etc. to pick an image from each page: 


https://wordpress.org/plugins/wordpress-seo/
https://wordpress.org/plugins/wp-open-graph/

There are quite a few other plugins which do that as well: https://wordpress.org/plugins/search/opengraph/