Apple - How can I extract Album Art from a track?

1. In iTunes select the song and press ⌘+I to Get Info.
2. Go to the tab Artwork and press ⌘+C to copy the Artwork.
3. Open Preview.app.
4. Select File → New from Clipboard from the menu or press ⌘+N
5. 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)

For completeness sake, in case anybody else comes searching for how to do the same thing on iTunes for Windows, here's the process:

1. In iTunes, select the song, right-click, and choose Get Info.

2. Go to the Artwork tab.

3. Then, click & drag the artwork to your Windows desktop. It makes a file.

That's it.