coverscout is an application by equinux that finds covers for your music collection. It can fix missing album and song covers in itunes. it embeds the artwork in the mp3 files, and will make your itunes look perfect :D
1) download and install
you can download the app from the equinux website, there is a demo available so you can try it out.
coverscout is also available from the app store
the installer is a .pkg file. simple to setup, you just doubleclick on the downloaded .dmg file and run the installer.