Since I know you run your own webpage, I'll give the technical explanation. My guess is that your browser defaults to overflow: scroll (or overflow: auto) for content too big to fit inside a block element, when overflow: visible is the standard.
I am seeing no scroll bars on Firefox 100.0 on Fedora Linux.
Interesting. I see two main takeaways from this:
1. This is likely a difference in how Firefox and Chromium-based browsers* render this.
2. A lot of images on the forum are evidently posted by Time Lords, since they're bigger on the inside.
*In theory all Chromium-based browsers should behave similarly, but given how many glitches HBO Max had for me in Chrome that vanished when I switched to Vivaldi, there are clearly differences.