Cover Characteristics: Book Covers featuring Keys

Guys, I think I have a problem. I think I'm just going to officially up my Cover Characteristics book choices to ten because choosing five? I can't do it, I tell you, I can't do it! Every single time I think to myself, I'm never even going to be able to find five covers, and then I end up with like thirty tabs of possible covers open at once plus five more of books I found when I inevitably got...