Two magnificent earth-moving grabs are poised at odd angles on the ground, their connecting rods silhouetted against a uniform sky. If it weren't for the characteristic tones and surface of an albumen print, you would be sure it was a modernist masterpiece by some 20th-century poet of steel. But it is anonymous, it comes from a functional engineer's report on the construction of a dam in Bihar, India, and dates from 1871. This exhibition, the British Library's first devoted to the photography in its own collection, is crammed with delights of this kind. There are famous photographs, too, but the quirks steal the show.

For example, the anthropometric photographs made by Maurice Vidal Portman, a colonial official, in the Andaman Islands in the 1890s. His platinum study of a scarified torso, cropped below the head, is a great nude. The ritual scars catch the light and modulate it as it falls across the curves of the body in a way that compares elegantly with the shadow contoured nudes of experimental photographers such as Man Ray and Erwin Blumenfeld a generation later. Yet Portman was no photographic sophisticate. In two other colonial studies of his, the hands holding the chequered backboard are visible to the left and right of the pictures like accidental symbols of control itself.