How can I extract Album Art from a track?
In iTunes select the song and press &#x2318;+I to Get Info.
Go to the tab Artwork and press &#x2318;+C to copy the Artwork.
Open Preview.app.
Select File &#x2192; New from Clipboard from the menu or press &#x2318;+N
Save the file to a custom location. (.png, .jpg, .pdf, .tiff, ...)


Alternative for 3 to 5 : just select the artwork, and drag and drop on you desktop (or elsewhere) (it will copy the original file there; eg : if the file inside was a PNG, you'll have a PNG, if it was a JPG, you'll get a JPG)