Ok, that makes sense now. Thank you.
I was just wondering if something could be wrong with how Discourse was picking the images and setting the og:image. But yes, if my Discourse works (even though not 100% perfect), then maybe something is wrong with what you said.
So, my question still is: the image being picked is always the topmost image in the topic? Is it how Discourse it built? Or is it randomly picked? And are there any specific requirements for it to pick the image in terms of image dimensions, etc? Just want to make sure that when it comes to my own topics, if I want to include images, I format them properly.