Uploading pictures for a Digital Market post

I am trying to post my first post to the Digital Market and want to include pictures in the post that are visible without a purchase. My understanding is that using the Attachments to attach the pictures will make them only visible after purchase. So I'm going to attach some photos to this thread so I can reference them from the Digital Market post.  Please let me know if there is a better way to achieve this.

I have been successful adding forums to another of my threads, but when I try to add this thread to a private forum I have access to, it doesn't seem to do anything.  Any idea why?

When the site was developed there was a question about what the behavior might be if a thread were in a public forum and a private forum.   Or in two private forums.   There were a lot of good points over expected behavior.  All of the expectations were reasonable, but seemed to require the system to do some sort of mind reading, or to have confusing configuration.  In the end, we simply said "no" and haven't come back to it.