Ack, never mind. I’m an idiot who doesn’t understand how Markdown works (yet).
However, HTML formatting to try to edit the line spacing works in the preview pane, but not in the post.
Editing the image size parameters added when you upload don’t do anything either.
This old meta.discourse thread makes it sound like this might be a feature added because people didn’t like the no space look. It looks like it’s baked into the CSS, but I’m not good enough at CSS to say for sure.
Turns out that a previous fix caused this! Sorry about that, your images should be working fine now!
Basically, a fix for a previous problem caused the behaviour you’ve noticed:
By setting vertical-align: baseline to post images, the images are aligned to the bottom of the baseline, which has a little extra space that in case of text, accounts for lettering that goes below it, like q, y, p, g and j. To fix it, I simply set vertical-align: bottom, which uses that extra space below.