Some years ago I wrote a column on this very topic. This little bit got me into some trouble:
Say it's Sunday morning. You stroll down to the local drugstore to score the morning newsprint fix, and while you're standing at the counter waiting to pay for it, you take a glance over at the book rack. There, prominently displayed, is Fabio, flexing his pecs on the cover of something called Passion Fruit.
You know immediately that the book so adorned is different from, say, Portrait of a Lady. Fabio is on the cover to make sure you understand that. Notice they didn't put him on the cover of Stephen Hawking's A Brief History of Time. Notice, too - and make of it what you will - that no one thought to put Hawking on the cover of Passion Fruit.