Quoted inline image attachement in forum posts not visible by guests

[wonderfulwat]

Step 1: Upload an attachment.
Step 2: Quote that post on a different page.
Step 3: View the post with the quote as (1) a logged in member; (2) a guest.

The logged in member can view the image as is. The guest only sees an "Attachment #" link.

Is this solvable? I know you can do it in class bbcode.php, but that messes up PDFs (or other non-image attachements).