So I know that apparently the map frame plugin didn’t work that well last time it was implemented (hopefully it’s not like a “we’re not considering this again” situation), but I found another one that might.
https://dev.bukkit.org/projects/imageonmap
I really can’t say about it being laggy or not, but it should at least work on 1.12.
We’ll be switching to 1.13 Soon™, and 1.13 makes a lot of technical changes so I doubt this plugin will work after the update.