Search for missing album artwork directly from Rhythmbox using the following ‘AlbumArtSearch‘ plug-in.
The add-on searches the web for album art/images of the currently playing song. From the resulting images, one can be set as the album art.
Whilst the plug-in is not automatic – it requires you to run it for each album/item individually – the ability to refine your search through the use of extra keywords and track filters makes locating the correct album cover more controllable than other ‘automatic’ methods.
The plug-in can be downloaded using the link below.
To install, extract the archive and move the resulting folder to ~/.gnome2/rhythmbox/plugins
Thanks to Jeddycakes