iTunes has long had what I call an “artwork player” window; it’s similar to the MiniPlayer, and you display it be clicking a zoom button on the MiniPlayer window. Here’s what the MiniPlayer window looks like, when it’s showing playback information, and when you hover your cursor over the window, it shows play controls.
The artwork player, that displays when you click the zoom button, looks like this:
The new window, however, harkens back to a window that was in iTunes back when the app displayed album artwork in the bottom left corner of its window. If you clicked that artwork, a window similar to this displayed. To display this window, Command-click the artwork that displays in the iTunes LCD, at the top of the iTunes winodw.
One of the differences with this window is the fact that you can zoom it. The artwork player is limited in size. Its width can only be a maximum of 400 pixels on a standard display and 800 pixels on a Retina display. You can resize this window by dragging from any edge, so you can make it tiny, but if you make it too narrow, the album art will disappear.
The new artwork player window, however, lets you even display it to fill the screen. Control-click the window, and you’ll see options to display the artwork at its actual size, to fit it to the screen, and to increase or decrease its size.
In the screenshot above, I’ve hovered my cursor over the window, to display the play controls; when you move your cursor away, it displays only the artwork. So you can leave this window open and have a larger version of the artwork for what you’re currently listening to visible at all times.