You can do this via scripting using nothing but Opus itself, but I don't think anyone has written a script to do it yet. AudioCoverArt in the scripting API includes the image's binary data which can be saved to a file.
On the other hand, if you only want it for MP3 files, this old solution I made should still work well, and it comes with buttons to integrate it into your Opus toolbars:
https://www.pretentiousname.com/WmaAlbumArtist/
There's also a forum thread about it, but the link above has more detail than the thread: