Books With Keys or Keyholes on the Cover
Many thanks to user Peggy and her excellent list: "Unlock a Good Book" https://www.listchallenges.com/unlock-a-good-book, from which I stole many of these titles. Some books have multiple covers represented.
avg. score: 9 of 224 (4%)
required scores: 1, 5, 8, 10, 13