Some of the others use https://repository-images.githubusercontent.com/3788728... and I couldn't figure out how to get there. We can go to the "simple" links, but i'll still going to put a rev in there, because we don't necessarily want to track what's latest.. because that could be abused if the repo is compromised and stuff.

If I put a rev in the "simple" url I get the url I used already.

The "simple" one is the one that's linked from the GitHub UI, so I've always used it. On the other hand, it looks like the API generates links with the form https://raw.githubusercontent.com/djhaskin987/groupme-purple/main/groupme48.png (and that's not API endpoint URL, but the one returned by it.) The other even longer one seems to be found with a few redirects, but I'm not sure how stable it is.
Of course, I don't think GitHub has any guarantees of stability for any of these, so...

so...? I still don't want to link to an image that could update to anything at any time.

You can still use the simple URL with a commit http://github.com/djhaskin987/groupme-purple/55ef8cb42f61d2bf174ba1132d971f9c249b8e41/groupme48.png

Oops, that should be: http://github.com/djhaskin987/groupme-purple/raw/55ef8cb42f61d2bf174ba1132d971f9c249b8e41/groupme48.png
(Why does RB not allow me to select the URL when it's in a code block?)

oh cool, I didn't notice the redirect!
As for the links in code blocks, no idea.

Gah, and I still messed it up since it should be https. Sorry.

And I'm so tired I didn't notice and just copy pasted :-D