If you purchase music tracks from the iTunes music store, each track will show cover art from the track's album when played. However, tracks you import into iTunes from your PC's hard drive might not have album art attached, which means the cover won't show in iTunes. Apple built a feature into iTunes that allows you to automatically download album cover art from the Internet, allowing the album art to load properly.
Open the iTunes software from the Start menu. Click "Start" > "All Programs" and select iTunes from its folder.
Select "Edit" from the top menu bar and choose "Preferences."
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Click "Store" to bring up iTunes Store preferences.
Check the box next to "Automatically download missing album artwork."