I will let my users have their own blog. Some will include an image, some not.
The post will be auto-published to Facebook and Twitter (I use EasyBlog).
I want the set-up to be that if they add an image to the post, that image will be "twitter:image" and "og:image" (or just "og:image" since, if I understand it correctly, Twitter will search for this and there's no need for duplicates). I will use content="summary_large_image".
If they don't use an image, I want to have a default image to show.
In "Open Graph -> Object setting" I only see the choices to have either "First content image" OR "Custom image".
So, I want a custom image to kick in if there's no first image.
How do I set this up?