coverlovin (Cover Art Downloader).

coverlovin is a CLI recursive directory album art downloader written in Python.

Coverlovin is a Python module for collecting artist and album details from a directory
hierarchy and downloading cover art from Google Images.
It can be used both as a module and as a standalone application.

CoverLovin employs Ned Batchelder's excellent id3reader.py module to obtain id3 tag info from mp3 files.
For convenience this module is included in Coverlovin tar.gz releases.

So... simply get your covers with:

$ coverlovin.py path-to-your-music-dir/