The thing is, that VOX app is using public sources to import Artist artworks and display them in Artist View, as there is no exact way to embed an Artist Artwork to your music files.
Music files you have imported cant be used as a source for Artist Artwork in Artist view.
Last.fm and their base of Artist Artworks, collected by community of Last.fm (and some of VOX members, as a part of the mentioned community), unfortunately, has been “closed forever” or “temporarily blocked”.
Now, we need to look for new, alternative sources to use them to populate the Artists view with proper artworks, which will be done, tested and introduced in the next versions of VOX app.
Also, we are looking forward to introducing new features, that will provide our users with the ability to import their own Artist artworks or Album artworks!