As DrSkipper asks: are you using the button, and what happens when you do?

I think all (most, anyway) of the pics I've posted in social groups, I've first added to the picture collection of that social group. I'm not sure that was necessary, though. When I tried including a pic from one of my albums, never uploaded to any social group, it worked fine (in the preview, anyway).

If your pic is from another site, it's possible that the site doesn't allow linking to their pictures from elsewhere. Can you make your pic show up in a forum post, or not?