He stands awkwardly as he lifts the spear, and he looks uncertain, as well he might. The young Zulu is pretending to be natural for a studio photographer of the 1880s. Behind him is a provincial-panto backdrop showing the kind of gentle forest that's filled with fairies and bunnies, not the jungle of Africa where Henry Morton Stanley could hardly see his hands.
In an image taken by a photographer this year, the face of a young African woman, brilliantly lit and blown up to more than twice life size, floats on a dark-sepia background in the manner of Robert Mapplethorpe. It is a colour photo, but the only colours, rich and deep, are blacks and browns and a bit of pinkish violet where the inside of her mouth meets her lower lip. We can see the whites of her eyes, clear and bright, as she coolly stares, and we can also see the three stripes of ritual scarification on her cheeks and forehead, as well as every hair and pore.
One's response to the first photograph is simple enough - amusement, sympathy, a feeling of mild superiority to the Victorians who saw in it nothing inauthentic or absurd. But while the second photograph seeks to win our respect and wonder as openly as the first seeks our condescension and curiosity, its aim is not so easily achieved. Are we seeing a great, dark goddess, or a woman who, to serve the photographer's purpose - artists being as ruthless as empire-builders - has been manipulated to follow the fashions in art and emotion? As we cross the lunar landscape of her face, noting every infinitesimal hillock and declivity, are we humbled by the fearlessness of her self-exposure or released from our awe by being able to know the imperfections of this woman's face better than she?
Such are the complications and disquiet provoked by an exhibition of 200 photographs of Africa and Africans from the past 150 years at Bernard J Shapero Rare Books in London. European guilt at the exploitation of Africa and the treatment of its people makes it all the more uncomfortable to consider the transformation of impoverished men and women into objects of art that change hands for thousands of pounds. African viewers have also been troubled by the images: before the show opened, one woman expressed such indignation at five of them that they were withdrawn. However, these supposedly degrading photographs - very small pictures of nude women sitting on a carpet or standing, framed by a cloak - are hardly different from larger images of other nudes in almost identical poses. They seem less disturbing than a picture of two very young girls who, naked but for a few beads, look vulnerable and bewildered before a painted ocean of stiff, curlicued waves, like actors called onstage in a costume from the wrong play.
These and other images from more than 100 years ago show how photographers with artistic ambitions would produce tableaux of odalisques of the sort painted by Ingres in the early 19th century and popularised several decades later by the orientalists. How many European purchasers of this contrived exotica, one wonders, noticed any disjunction between the props and poses of the Maghreb and the skins and shapes of Africans from much further south? The images that are most genuinely exotic were taken in 1856 in Algeria. These show women, in brocade kaftans and beaded headdresses, who could be posing for Delacroix. Perhaps they did.
In several portraits the echoes of other styles and ages can be heard. A profile of a young Congolese girl, beads piled at the back of her head in the shape of a Renaissance coif, a large teardrop-shaped bead hanging from an ear and cords crossed between her breasts, would, if the breasts were covered, be a modern-day Piero della Fran cesca. Irving Penn's five Dahomean girls, also bare-breasted, have their necks and shoulders covered with white paint or ash in the exact shape of the collar of a nun.
Sometimes, however, the aim of the pho tographer was to extirpate the exotic, with its connotations of sensuality and ignorance. One image of a middle-aged couple in Bechuanaland demonstrates the benign influence of "Christianity, commerce and civilisation", the mantra of the English modernisers. The two look as if they have been civilised at riflepoint into a three-piece woollen suit and a stiff, shiny dress that gives the stout black woman not so much the appearance of a Victorian cook as the look of a stove with arms and head.
Of course, white Europeans of the same era were also constrained, in photographs as in reality, by the formality of their culture. As this gradually dissolved during the 20th century, Africans who had previously been regarded as childlike in their expressiveness were instead considered healthy and spontaneous, the way Europeans would like to see themselves. Who could not warm to Mirella Ricciardi's 1968 photograph of two lithe teenage girls chatting, far more attractive with their Mohican haircuts than any similarly coiffed and posed punks on the King's Road? The photographer has emphasised their bent knees and elbows, their little triangular breasts, with the oblique line of the sand dune on which one leans; like the photographs in the glossy magazines of the time, this picture blends consummate elegance and good cheer, qualities that for a brief period were compatible.
If European viewers are pleased at being able to identify with these Africans, a picture hanging nearby will jolt them with its mystery. By Malick Sidibé, a Malian photographer who won the Golden Lion for Lifetime Achievement at the 2007 Venice Biennale, it shows a small, grinning boy who has bulked out his ragged jumper with something that gives him the silhouette of a heavily pregnant woman. That is impishness we can understand. Next to him is a boy whose face is covered in white paint and his body with white blotches and lines that make him look like a living skeleton. There are feathers on his pointed hat and a white staff in his hand. He also smiles.
That image, so startling with its simultaneous rejection and embrace, is rivalled by one other as a metaphor for Africa: with so many differently shaped features, natural or created, in the exhibition (the members of some tribes distend their lips and earlobes), it takes a moment to realise that this dark face across the room is really a mask. Its tone in the black-and-white photograph matches that of its wearer's shoulders, and, because a deep shadow falls where they meet, we cannot see where man ends and mask begins.
"Tribal Portraits: Vintage and Contemporary Photographs from the African Continent" is at Bernard J Shapero Rare Books, 32 St George Street, London W1, and runs until 23 December. Details: http://www.shapero.com