It's probably the image proxy the forum uses.
HTML Code:
<a class="proxied-img-link" href="https://i.imgur.com/ZCyWjcr.png" rel="nofollow noopener">
<img class="proxied-img" src="https://forums.alliedmods.net/image-proxy/a08b18a068c6f5640bdff20f8d185f8de49069f9/68747470733a2f2f692e696d6775722e636f6d2f5a4379576a63722e706e67" alt="" border="0">
</a>