Album Art Changer Pro

Pro version allows automatic bulk update of album art. It is also free of ads.

Downloads and sets album art to your music collection. Get art search result for any song. Also allows you to edit tags.

Features:-
Set album art per song basis instead of album
High quality Images
Bulk update missing album art
Can save both to tags and android database
Saving to tags lets the cover art to persist while moving the mp3 to different computer or device
Choose cover art from gallery
Edit tags such as title,album,artist
Save Album Art to Gallery
Play Songs
Delete Songs

If your music player doesn't detects changed album art, try clearing it's cache by going into Settings->Apps->Your Music Player->Clear data

If your music player shows duplicate album art, then they use Mediastore database which is limited to 1 album art per album. Ask them to use Tags for showing unique album art.