The usual approach when designing the cover for an autobiography or biography, at least when the subject has any sort of fame, is to use a big, dull, flattering studio portrait photo. Do a Google Image Search for 'biography covers' for endless examples. It's the obvious way to flog a book about a famous person, and any designer who tries to go against the publisher's marketing people is almost always going to be fighting a losing battle to do anything different or more interesting.
That's why covers like the following, for physicist Stephen Hawking's memoir, are so welcome. Even people who know nothing about black holes or A Brief History of Time are likely to know one thing about Hawking: his physical condition. To show an image that goes against that, and in which the man himself is not immediately identifiable, is clever and intriguing.
All credit to Kathleen Lynch of Black Kat Design for the cover.