If a DGBBS posted picture is from a website such as Photobucket.com, as most are, such picture will only be viewable in the topic as long as the URL link to such picture is valid.
If the author subsequently either moves or deletes the picture on Photobucket.com, the URL reference to the pic in the DGBBS topic is rendered invalid, and the pic will disappear from all further attempts to view it. This is usually represented by the icon and dot you describe...
This is why many older topics don't have all the original pictures in them.
