Thanks Gabi. That certainly makes sense, to thwart the evil spammers!
Note that I hacked around this in my post by using imgur links. What I was able to do is create a image on imgur.com, but then copy/paste the URL of that .png file on imgur directly into the post. Then the images were directly viewable. I think that was done prior to any admin seeing and approving the images.
Images and videos must first be validated by a forum moderator and only then can they be viewed.
Note to the administrator of this forum (where else should I be able to report this?):
I spent a lot of time uploading images into my post:
But when I clicked on that after the fact, they came out as triangles.
Here is an example:
What I had to do is upload my screenshots into imgur.com and then copy the URL, and then paste that URL.
That seems like it is a defect in the website.