Just recently I had a phone call from Thom Abbott because he was trying to add a post to his facebook business page and the photo that was showing up when posting the short url wasn't the photo from the post, and facebook wouldn't let him upload a new photo like it would in the past.
He wanted to put the photo he wanted there and it just wasn't happening.
What to do what to do?
Well use the Share button.
Yes, right now the way to get the photo you have (it will allow the first photo from your post) in your post you click the share button and then arrow to the photo you want to display. I just shared a post I write last week as a last minute reminder to folks that we're having a local festival tomorrow. The photo is from a previous gathering. and it displayed as shown on the photo to the right.
I miss the "upload a photo" from facebook too, but at least I have figured out how to get the photo I want from an AR post to show up on Facebook.