I have created a fork of this extension which integrates with Extension:PageImages, so that if both are installed, the intelligent prioritized and automated image selections made by that extension can apply to the og:image property in lieu of other forms of specification (this fork also fixes the php exceptions that are thrown by MediaWiki 1.24 if this extension is installed unmodified, due to there not being a form of Title::newFromDBkey that accepts two parameters). You can find the source code for the customized branch here.
Topic on Extension talk:OpenGraphMeta/Flow
Amazing, and amazing timing -- have been updating my wiki for OG starting a couple of days ago, and was scratching my head about how to sort out og:image without wrangling editors into manually doing it. This seems to work great! Only thing I wish I could do now is a mass-resave of articles on our wiki so that it could populate this faster.