For a long time, I’ve been confused on just how to add missing album artwork to multiple songs in iTunes. I know you can automatically have iTunes fetch album artwork, but it is probably the case that not all of the files in your library will be available via iTunes. Hence, no automatic artwork. The artwork must come from an outside source. In my opinion, the best cover images can be found on the Amazon.com Music site.
You can add artwork to any song that is currently playing by dragging a picture of the album cover over to the “Now Playing” window within iTunes. The problem with this is that the individual song must be currently playing. The problem is that I want to add a album art to all of the songs on a particular album! You cannot simply highlight all of those tracks in iTunes and use the “Now Playing” window. You have to select a group of songs and then choose “Get Info” and then drag the new artwork from your computer or web browser into the “artwork” window within the Get Info dialog box. For more information, see Apple’s support topic on this issue: http://support.apple.com/kb/HT1409.