Neutron builds own media library and searches for an album art in:

  1. Folders where music files are located;
  2. Metadata (tags) of the music files.

On iOS Neutron will source album art from the iTunes library for the iTunes tracks. On Android Neutron does not use laggy internal system media library and therefore please make sure you have images inside the album folders or re-tag music files and attach images to their metadata. You can use excellent free application for re-tagging your music files - Mp3Tag.