Retrieve Album Art

I have searched and can not find what I am looking for, though I am sure this has been asked a million times before.

How long does it take to retrieve the album art for a library of music files? Where does this album art come from?

In my collection I have just under 500 albums with a total of 6000+ MP3 files. Each album is stored in a folder by genre.

Thanks,
Mike

[zip]

It can be embedded in the music files or stored as a separate jpg image. Serviio supports both.