Anyone who’s spent time leafing through the pages of a coffee-table book knows that these oversized volumes are often art in their own right. The German publisher Gerhard Steidl, who specializes in books of photography, puts it this way: “Buying a complete set of Robert Frank’s prints from The Americans is today nearly impossible (even if you had the money). But anyone can go out and buy the book, knowing that the photographer oversaw and approved it as a multiple of his work.” This exhibition celebrates the photo book’s democracy, and also its value as an extension of the artist and the artist’s message. —J.V.