CoverChooser is a small application, that searches albumart at the internet and downloads your choosen file. At the first run of CoverChooser, it will be automatically integrated into your Nautilus-scripts.
By applying the script at a mp3-file (or a folder that contains mp3-files) the script will use the mp3 metadata to get the interpret/album-info. It saves the selected file as “folder.jpg” (or folder.png).
Links : http://gtk-apps.org/