As a species, photographers are insatiably curious – positively nosy, one might say. And we are all photographers now.

Curiosity courses through humankind’s genes – a natural defence mechanism. But it takes a particular form in photographers, defence turned into attack in the urge not so much to be wary of, but to spy upon our fellow human beings. The resolutely unsentimental Walker Evans mentioned “spy”, along with “tinker”, “reporter”, and “voyeur”, in his definition of a photographer. He also remarked that photography’s primary mission was “to recognise and to boast”.

In recognition we confirm the fundamental human need to look, and make sense of the world. Boasting of that necessity, however, is another matter, marking a darker, more troubling aspect to the photographic act.

Predictably, but pertinently, Evans’ great “spy” pictures, his subway candids shot through the folds of his overcoat, open Tate Modern’s new photographic blockbuster, Exposed: Voyeurism, Surveillance & the Camera. The subway portraits are accompanied by Phillip-Lorca di Corcia’s updating of this supremely voyeuristic mode, his large-format candid street portraits, made when his subjects crossed an electronic beam and unwittingly tripped a shutter.

[Subway Passengers, New York], 1938 © Walker Evans Archive, The Metropolitan Museum of Art

Diane Arbus famously remarked that she thought of photography “as a naughty thing to do”. Like Evans and Arbus, Henri Cartier-Bresson was well aware of the medium’s “naughty” side. His photobook masterpiece, published in America as The Decisive Moment, was originally titled "Images à la Sauvette", images taken “on the wing”, or “on the fly”, a dubious connotation not so different from the novelist Frederic Raphael’s characterisation of photography as a “sly” art.

But what art, if any good, is not a little sly at heart?

Slyness, naughtiness (and worse), frame the central premise of Exposed, the first photographic show under the aegis of Simon Baker, the Tate’s first curator of photography. Originated by Sandra  Phillips of the San Francisco Museum of Modern Art, the exhibition asks just how sly are photographers? And crucially, how sly are the uses to which medium is put, not just as a vehicle for photographers’ self-expression, but as a social tool, as a means to control society?

The exhibition, both ambitious and topical, is about the implications of looking at ourselves and others, and is divided into five broad themes relating to scopophilia and the camera. They are candid photography, celebrity stalking, sexual voyeurism, witnessing violence, and surveillance.

As Sean O’Hagan of the Observer has remarked, Exposed is essentially about photography as “a licence to spy and pry, to transgress, shock, provoke, and above all, invade the privacy of others”. As the show’s opening wall label indicates, the primary intention of the curators is to examine “photography as an invasive act that, whether by intention or effect, challenges common ideas of privacy and propriety”.

O’Hagan also makes the point that the show is about the politics of looking, a highly relevant issue as, firstly, it becomes more and more difficult for photographers to make much of the work shown here, especially of the candid, street photography kind – a point made with increasing frequency by readers of this journal.

And secondly, just as individual photographers’ freedom in public places is under threat, others, notably governments and large corporations, have given themselves leave to photograph us from afar. Voyeurism and surveillance. We might say they are two sides of the same coin – voyeurism being personal, the product of a wilful individuality, while surveillance is impersonal, the product of a stealthy anonymity.

Frequently, the boundaries between voyeurism and surveillance are indistinct, and overlap. Merry Alpern’s series, Dirty Windows (1994), naughty goings-on photographed clandestinely through the bathroom window of a New York sex club, is considered “art”, perhaps voyeuristic self-expression, maybe a critique on the business of voyeurism, although it might be regarded as reportage if taken by a photographer with different intentions. However, if taken, say, by a police photographer, they could be part of a surveillance operation to apprehend the instigators of the drug dealing observed in some of the images. Often, intent and context makes the crucial difference. Or does it?

Untitled (Atlanta) 1984 © The Estate of Harry Callahan, courtesy Pace/MacGill Gallery, New York

Equally, the boundaries between modes of photography are blurred, almost impossibly so, in Exposed. The big names of art photography, from Evans, Cartier-Bresson, Brassaï, and Harry Callahan, to more recent stars like Sophie Calle and di Corcia, are mixed in with lesser lights, to those whose names we hardly know, and good old “photographer unknown”. Everything from snapshots, commercial photography, documentary and art, to anonymous agency photography is included – necessarily so. But it makes for an awkward, aesthetically uneven exhibition, the fault of the subject, and the material, not the curators.

Also, as seems to have happened to O’Hagan, I found much of the show a little tame in terms of the naughtiness stakes, especially the section on sexual voyeurism, and, to a lesser extent, the section on violence and the camera. This may or may not be down to the curators and their sense of propriety – or to a critic’s jaded palate. But promised an exhibition that would shock and provoke, I was neither shocked nor provoked, although certainly intrigued and stimulated into thought, which is probably a healthier reaction. Roland Barthes said, after all, that “photography is subversive not when it frightens, repels, or even stigmatises, but when it is pensive, when it thinks”.
Images transfix

I don’t think this sense of tameness was simply a result of critic’s déja vu, but something more fundamental. I think it may also reflect Susan Sontag’s point, made in her book On Photography (1977) – an extremely prescient point in pre-internet days. Writing about the effect of increased exposure to pornographic or violent photographs, she remarked: “Once one has seen such images, one has started down the road of seeing more – and more. Images transfix. Images anaesthetise”.

This brings us to a crucial issue. Sontag’s “road” has become a 12-lane superhighway. It’s the issue – perhaps largely unseen, but certainly not unspoken – that hangs over Exposed, just outside the galleries, like the seven-eighths of an iceberg that lies underwater – the ubiquity, and incredible proliferation of photographic images in our society thanks (if that is the right word) to the internet. Not just in terms of numbers, but in terms of the almost total lack of control regarding their content.

No wonder I found Exposed a little tame. Out on the Web lurk sickening images of sexual practices and violence that are probably too graphic to show in any museum, which prompts another question. And that first wall label makes another interesting point – has this proliferation of electronic imagery anaesthetised us in another way, not only inuring us to all kinds of voyeurism, but bringing us to a situation where we meekly allow cameras to watch every move we make, 24/7?

Exposed throws up lots of questions. As the internet, in the name of providing information, allows us to bear witness, does it make voyeurs of us all? For instance, will the death of Iranian pro-democracy demonstrator, Neda Agha-Soltan, splashed across the Web to become “the most widely witnessed death in history”, make a difference, or provide just another vicarious, voyeuristic thrill?

The answer is probably a bit of both, with the balance probably tipping, unfortunately, towards the latter. It’s the old-age reportage dilemma, and the usual answer, that bearing witness is vital – though it still must surely pertain – becomes ever more fraught with problems.

What Exposed cannot really demonstrate on the wall, is intention and effect. Even with wall labels, these photographs are somewhat out of context and partially muted. The show, however, can at least ask the questions, although the answers are hardly clear-cut.

One early image at the Tate comes from Jacob Riis’ work on the New York poor, pioneering, crusading photography, intended to change social conditions. A woman sits, as if blinded by the photographer’s flash, beside a large plank of wood, while an arm and hand in the image’s foreground points at her.

It’s a bizarre photograph, demonstrating the inherent surrealism of the medium, certainly, but also indicating with unsettling clarity the whole process of a photographer photographing the poor as “other”, like a specimen from an ethnographic expedition. It seems to confirm Max Kozloff’s observation that “nothing is more typical of so-called concerned photography than the brutality of its compassion”.

Yet there is compassion throughout Exposed. Often it goes hand in hand with a psychological distance bordering on the disinterested, or with a curiosity approaching the voyeuristic. Some of the very same images included in this thought-provoking and important exhibition could take their place in a show examining the medium’s compassionate side.

Of course every single viewer has a different reaction to a photograph. Faced with some of the images I found myself thinking, voyeurism, what voyeurism? A kid brought up with the internet might well think that about much of the exhibition. One photographer’s voyeurism is another’s bearing witness. One photographer’s intrusion is another’s good intention.

Exposed rightly raises issues, many of them deeply troubling, about the intrusive nature of photography. While viewing the exhibition, and pondering it, we should also remember that the photographic act can also be one of concern and empathy.

Exposed: Voyeurism, Surveillance & the Camera continues at Tate Modern in London until 03 October.