I got my solution to the silver challenge mostly satisfactorily done. I added an attribute. I installed a button next to the tags button to favorite a picture. I created a segue to another navigation controller/collection view where I could display my favorites by themselves. So far so good.
I then noticed if I restarted the app and it reloaded the persisted objects, that I had two copies of each favorited photo, one of which had the favorite attribute true and one of which had it false. At this point I haven’t been able to sort out how to get rid of the false one. Of course when I unfavorite a photo I wind up with three copies: two false and one true. The documentation on how to delete objects from the NSManagedObjectContext is hard to find.