If I opt to automatically download missing artwork via ITunes....?

theres no easy way. its a pain in the ***

I have downloaded via iTunes with no problem, whether I purchased at iTunes or not.

Also, I go to Amazon, seek the album, click enlarge on the photo, and being on a Mac, i drag the image to my desk top.

Put it in a file ('album covers for iTunes) on my desk top.

Open iTunes, go to the subject (might be a radio theatre product for me), do command key and letter i, or 'information', go to the art work tab and add your down load.

If somewhere, on a Mac, you run into a protected image that will not drag to the desk top, place your curser at the top left of the image you want, with left hand, keys 'command,shift, hold the two, add #4 and hold, drag with the mouse over the image, let go at your chosen edge. If your sound is on, you will hear a camera click, and you have a copy of the item on your desk top, in jpg. Occasionally I have had to do this more than once to get the image which may be just the mystery of computers.