Karl Baden is a photographer who teaches at Boston College. Not surprisingly, he likes photographs. He also likes browsing in used bookstores.
''I started noticing people had been putting photographs I recognized on book covers: fiction, poetry, textbooks," Baden says. ''After a while, I thought I'd investigate this a little bit. I tend to be fairly obsessive. So I just started buying them up."
That was years ago. Baden estimates he now has more than a thousand such books. Which photographer's work most frequently shows up? ''Man Ray is the most popular -- or at least the most popular I've found -- whereas Ansel Adams I've found only two or three covers," he says. ''Walker Evans has a lot. So do Bill Brandt, Brassaï, Karl Blossfeldt, Atget. Nan Goldin is getting up there."
Baden was struck by the fact that certain images would get used multiple times, often for very different books, and in very different ways. The same photograph might be cropped or tinted or have type on it. In those various uses, the covers became a kind of history, at once revelatory and warped, of not just photography but also book design, literary taste, and marketing considerations.
A small exhibition drawn from Baden's collection, ''Covering Photography: fifty-five books, twenty-five images," runs at Harvard's Carpenter Center through Nov. 13. It conveys just how warped and how revelatory -- as well as once again raising that age-old question: Can you judge a book by its cover?
''Well, no," Baden says, ''but you can certainly buy a book by its cover."