"Tagger MP3" is a free app that allows you to edit tags of audio files like MP3, M4A and OGG.
You can select from the web the Cover image.
You can use it to organize your audio files by entering data that are read from the common MP3 players.
This app also allows you to search for the covers of the album.
You can edit the tags of a single track or of an entire album of music.