How do I get artwork for my itunes library?

I had the same issue and then I did this:

1. Open iTunes
2. File > Library
   1. Update iCloud Music Library
   2. Organize Library > Check the Consolidate files box > OK
   3. Get Album Artwork

And when I was all done, everything was just like I wanted it and the album artwork was all imported.

Click File, Library, Get Album Artwork. It will only work if the album name, artist name and song name match a song in the iTunes Store.