How do I add album artwork for songs that are not in Apple's catalog of music?

I recently started my Apple Music subscription and I added some music to my library that is not available in the Apple Catalog because they are live recordings that I made myself. I want to add artwork to these recordings because it is much easier to search for music on my devices when there is a picture. When I imported the recordings to my library on my mac, it automatically started updating my iCloud Music Library and now when I try to add artwork in the Get Info tab, the album will just "blink" when I hit ok, without actually adding the image file I selected. The audio files are AIFF, and before I had Apple Music I had no issues adding album artwork to files in this format. The support pages about album artwork are not helpful because they assume the songs you want artwork for are in the Apple's catalog.