Chronologically, one of the last images in Beat Memories: The Photographs of Allen Ginsberg, in the West Building of the National Gallery of Art, is a portrait of Bob Dylan taken in New York’s Tompkins Square Park in 1992. This one photo demonstrates what’s great about this exhibit, but also what’s problematic about it. On the one hand: it’s a picture of Bob Dylan made by Allen Ginsberg, one of the great voices of the counterculture as seen by another, a pair of aging veterans of a scene which by then had become positively mainstream, if not thoroughly commodified. But is it the visual art, or the cultural gravitas, that makes this an great photograph?