Are you being watched?

Most likely. Surveillance, especially by camera, is a fact of modern life.

There's still a difference between private moments and the public scrutiny that accompanies fame or notoriety. But just within the past decade, the ubiquity of cameras has redefined public and private life, sometimes with tragic consequences. The recent suicide of a Rutgers University student after his roommate posted surreptitious videos of the boy in a homosexual embrace raised a host of questions about the brutal consequences of unwanted cinema verite. And since every image goes public eventually, it's only a matter of time before the photos of Osama bin Laden's body go viral.

A strange new exhibit, opening Saturday at Walker Art Center, examines some of the darker psychological angles of camera culture as it has evolved over the past 140 years, though it is disappointingly mum on hot-button contemporary situations. Its premise is that voyeurism is now, and always has been, the essence of photography.

Called "Exposed: Voyeurism, Surveillance, and the Camera Since 1870," the show features about 150 mostly black-and-white images, including news and documentary pictures; paparazzi shots of celebrities; sex and bondage photos, and images from spy and security cameras. Spanning more than a century, subjects range from a heap of sepia-toned skulls beside a Civil War grave to a blurry snap of Paris Hilton sobbing in the back of a police car.

While a few of the more recent color pictures are as large as posters, many of the images are about the size of postcards, which oddly subdues their impact and simultaneously draws viewers in. A little 1930 photo of a Texas lynching by an unknown photographer, for example, is horrific and unforgettable -- first, because the hideously burned body of the victim, George Hughes, dangles from an ashy tree in the center of the picture and, second, because four of his likely killers, all bug-eyed white guys, pose with the corpse. Who took the photo and why? Was it to document an atrocity so the perpetrators could be brought to justice? Or, more likely, was it intended as a ghoulish souvenir and warning card?

Organized by the San Francisco Museum of Modern Art, the show offers no answers to such questions, leaving viewers to draw their own conclusions about what curator Sandra S. Phillips calls the "amoral allure" of violence. Smaller modern cameras enable us to more easily invade others' privacy, she writes, and to "look at sex or death with the same prying curiosity."

Five themes

The Walker's installation is loosely arranged in five thematic sections. The first, "The Unseen Photographer," includes images taken anonymously or on the sly. Some are intended to arouse sympathy, like Dorothea Lange's 1933 "White Angel Breadline, San Francisco," depicting a destitute man in an almost prayerful pose. Robert Frank's 1954 shot of a legless man wheeling down a New York street on a scooter is a different thing entirely, a freak sight that no polite eye would have dared engage. Walker Evans' photos of subway riders, taken surreptitiously, are candid but boring.

"Voyeurism and Desire" offers a predictably kinky selection of bondage pictures, historic prostitute and transvestite imagery, and contemporary Peeping Tom photos of sex acts snapped through dirty windows. As recently as 1971 Japanese voyeurs apparently crept through park bushes at night to spy on couples in flagrante even as photographers -- in this case Kohei Yoshiyuki -- took pictures of everyone involved. Truly weird.

The third section, "Celebrity and the Public Gaze," proves that even famous people once shunned the camera. Greta Garbo glowers and Jackie flees. Anita Ekberg's husband lunges at an intrusive photographer. Even Dick and Liz, those consummate camera whores, glance around furtively before nuzzling in a series of grainy paparazzi pictures.

Not surprisingly, "Witnessing Violence" is a harrowing section of jumpers (fire, suicide), mutilated bodies, assassinations, executions, lynchings and Vietnam. Some of the 20th century's most infamous photos are here, including Tom Howard's sensational 1928 picture of murderer Ruth Snyder shaking in an electric chair as a lethal jolt hits her, plus two Pulitzer Prize winners: Eddie Adams' 1968 picture of a South Vietnamese general executing a Viet Cong infiltrator, and Nick Ut's 1972 picture of terrified Vietnamese children fleeing a napalm bombing.

Explanatory labels contextualize some pictures, but most are left hanging. Staring at a photo of a young, naked amputee in a Phnom Penh hospital, circa 1990, you want to know his story but, given nothing, you are mesmerized by the button-stubs where his knees would have been. What is the point of showing such things without the thousand words needed to explain them? Without context, humanity is sacrificed to sensationalism, and images lose their moral equilibrium.

The final section, "Surveillance," covers political territory with clandestine FBI photos of Russian spies, aerial images of missile sites, surveillance pictures of bodyguards, checkpoints and empty parking lots from the "Blow-Up" school of cinematography. Though fascinating in a creepy way, too many of the pictures are by their nature murky, indistinct, poorly lit and unintelligible to anyone but a spymaster.

Topical but unsatisfactory

The issues raised in "Exposed" are undeniably topical, but the show's thematic treatment is overly broad and, ultimately, unsatisfactory.

To describe such a variety of subjects and approaches to picture-making as voyeuristic is misleading because it ignores both the photographer's intent and the way the images were understood by viewers. Voyeurism is obvious in the sex, celebrity and surveillance pictures, but attributing it to social documentary and war photos is facile and overreaching. Photos of lynchings, Nazi victims and 19th-century immigrant squalor beef up the exhibition's claims to gravitas, but by stripping them of cultural context, the show trivializes the images by implicitly accentuating their sensationalistic features -- bullets to the brain, nooses round the neck.

Pictures of violence and degradation have Phillips' "amoral allure" only when they're treated as tabloid fodder. Photos, after all, are documents; interpretation is a curatorial art.