I don't know if anyone noticed this, but when I clicked on the image in this topic, its size changed ---> https://www.altcoinstalks.com/index.php?topic=318223.0
Surprised you are just getting to know about this features, it's one that have been for a very long time, atleast. I've noticed this since 2020 when I joined this forum, you can resize an image you are posting to whatever smaller size to fit in the page of this site, which sure will appear at the size you attribute to it, but if for any reason, the images can't be seen clearly, a user can click on the image ones to enlarge it, and ones again to take the image back to its normal specified size, cool feature.
Now, speaking on making the small sized imaged the default setting, I don't see how that can work, because some images come at an extra large format where if no resizing elements is attributed to the image, it will still appear too large even when there is a default forum setting that automatically resizes images to look smaller when posted, and this means that, the user posting the image will still have to resize the image him or her self.
This is my opinion, if I understand what op is suggesting clearly though.