I'm not sure if any forum allows this, but it's a quite common web page thing and that's frames. Specifically to use them as galleries. Would be nice to build an album off-site and pop in the frame of it with clickable thumbnails. It would allow the images to be larger.
This is a gallery for example
And to embed it you use this code that I'll put in the "code" indicators on the formatting tools line of this topic editor:
<iframe class="imgur-album" width="100%" height="550" frameborder="0" src="http://imgur.com/a/dLGz2/embed"></iframe>
It says next to the text box that I am typing the message into that HTML code is off as a forum option but am not sure if this is considered HTML code.