Actually, I should have read more carefully. From that same S.O. thread, the bottom down-voted comment. It seems a bit hacky, but it works. And this seems to be the equivalent of copying the file directly from Finder, which gets the furl and pastes as the actual format of the file (in my case, jpg):
osascript -e 'tell app "Finder" to set the clipboard to ( POSIX file "<PATH_TO_IMAGE>" )'
This doesn’t work for copying images into this forum for example. But that’s ok for now. It works for pasting into documents or note-taking apps.