Although iTunes has a feature for automatically fetching album artwork, there are likely going to be times that you’ll still want to add artwork manually to your tracks, especially for more obscure tracks that you’ve imported from your own collection. Unfortunately, with the redesign of iTunes 11, the long-established artwork pane in the bottom left corner disappeared, and with it one of the easier shortcuts for adding and removing album artwork.
Fortunately, however, all is not lost, and you can still add artwork to multiple tracks through the track info dialog box. Simply select one or more tracks and choose Get Info from the iTunes File menu.
If you’re working with a single track, you’ll need to switch to the “Artwork” tab, while with multiple tracks selected, an “Artwork” section will appear in the main Info tab. From here, you can drag and drop an image in from Finder or Windows Explorer, or paste an image in from the clipboard using CTRL+V (Windows) or CMD+V (Mac).