https://github.com/desbma/sacad

SACAD is a multi platform command line tool to download album covers without manual intervention, ideal for integration in scripts, audio players, etc.

Since version 1.6, SACAD also provides a new command line tool, sacad_r, to scan a music library, read metadata from audio tags, and download missing covers automatically, optionally embedding the image into audio audio files (since version 1.9).

Since version 2.0, SACAD has been rewritten to use the asyncio framework, which typically results in ~40% faster processing for sacad and 600-700% faster (yes, 6-7x faster!) for sacad_r.