@billbennettnz You should be able to use https://cards-dev.twitter.com/validator to test in advance which photo Twitter will pick. Most plugins that control the og:image will usually default to your "featured photo" if one is set, otherwise they often default to a pre-settable photo if your post doesn't have one.
I'm sorry, I'm wrong. It has changed. I can see why now. That's fixable.
Bill Bennett, Jul 16 2017 on twitter.com