A popular request is for Asunder to download and display album art. Not a technically crazy request but I'd need to figure out where to get it, download it, display it, and save it in tags when supported. All that together makes it probably a few days of work.
Hi Andrew! If you still have an interest in providing support for album art, there's a collaboration between MusicBrainz and the Internet Archive, called Cover Art Archive.
The API they have documented seems to be HTTP based.
The tags for embedding the images will likely have to be ID3v2 based. But that too seems to be documented:
Either way, thank you for Asunder. Its been a great tool.
Unfortunately I've got to reply the same way I usually do: I just don't have the time to implement this but I'll be happy to accept a working patch if someone else can write the needed changes.