I want to provide more kudos. I recently deployed David Taylor’s most excellent “Topic List Thumbnails” theme component. It’s awesome that I can generate a thumbnail to accompany any topic - and furthermore, that I can choose the image from which to generate that thumbnail with a “|thumbnail” tag at the end of the image declaration.
Perhaps it’s because the underlying architecture draws on this tag for og:image as well as for the theme component; but I was delighted to find that when I changed the thumbnail, it changed the OpenGraph property for og:image as well, and hence what rendered in Facebook. Two birds, one stone, and like that! 
Great stuff!
Dan