I'd say ones you've taken yourself.
If the image is copyrighted strictly speaking you would need the owner's permission to post it. Without this permission the poster puts both themselves & the forum owner at risk of being sued. Don't know how facebook gets away with it. I know of one forum where I was a member which closed down under threat of being sued. The outcome of the suing is almost irrelevant, it,s the process that those being sued get dragged through which makes the risk more than it,s worth in most cases. In this instance it is Andy's call.