Remember kids, PNG is like TNG but for screencaps. Friends don't let friends use JPEG.
Not at my PC right now. I will try to fix it later. An easy way to find the screen grab is to search for Sherri Townsend
I think Lemmy just compressors images that are in the comments in a way it doesn't do for posts. It's really weird and kind of broken behaviour. You are probably better off hosting it somewhere and then just linking to the host.