Philip Kennicott is the chief art critic of The Washington Post and the recipient of the 2013 Pulitzer Prize in criticism.

In the Odessa Steps scene of Sergei Eisenstein’s 1925 film “Battleship Potemkin,” a boy no more than 3 or 4 years old is shot by czarist troops. Bleeding, he falls to the ground, where he is trampled by a frantic crowd fleeing the massacre. His anguished mother gathers up his broken body, showing it to the troops, and the camera, making a three-fold argument: Have pity on my son; have pity on my people; have pity on humanity.

In 1925, film was still a new medium, with astonishing power to shock, and humanity believed, naively, that it might set a standard for basic decency in the governance of people and the relations between nations.

The posture of the grieving parent, holding up a dead or dying child to provoke the conscience of the world, has appeared again — in images from Syria that show the consequences of a chemical weapons attack allegedly committed by the regime of Bashar al-Assad. In a compilation of videos shown to the Senate Intelligence Committee on Sept. 5, a man addresses the camera as he holds the limp body of a child — probably a girl. The shirt is pulled up, the mouth slightly open, the hair disheveled. She is clearly dead, though close enough to life that one can imagine she might wake up, shake off her torpor and go out to play.

In a speech to the nation on Tuesday, President Obama referred to those videos and adopted the same posture, rhetorically holding up dead children as an essential casus belli in his case for a strike against Assad’s government. Seven times in his brief speech he referred to children, “children lying in rows, killed by poison gas,” “a father clutching his dead children, imploring them to get up and walk,” “children writhing in pain and going still on a cold hospital floor.”

Even more striking than his stark description was his insistence that we look, that we seek out the videos — available through a link on the White House Web site — watch them and allow their power to shape our judgment about possible military intervention in the Syrian civil war.

And yet, no matter what one thinks of a military strike against Assad, it is remarkable how little outrage these images have provoked. The president repeated the word “children,” brought his listeners back to images of suffering young people, in part because those images haven’t sunk in. In some fundamental way, we haven’t really seen them.

But it’s not clear that even if we did look at these dark, grainy and chaotic videos, that would change things. Already, Americans overwhelmingly believe that Assad used chemical weapons, yet public opinion remains resolutely opposed to military intervention in Syria.

We have arrived at a double crisis: a dissolution of agreement about what is civilized behavior and a dissolution of faith in the meaning of images — a crisis of politics and a crisis of representation. Given how closely photography and video have been linked to defining those international norms, this is a frightening moment.

Images of children suffering form the ultimate emotional argument, compelling us to move from sentiment to action, from the particular to the universal, from passivity to engagement. In the past century and a half, we have credited photographs of dead, wounded or starving children with galvanizing political opinion — against an unpopular war in Vietnam and for humanitarian interventions in Africa.

Cecil Beaton buoyed spirits during the London Blitz with an image of a wide-eyed girl in a hospital bed, clutching a crudely made doll. But we have seen even worse: children covered in the dust of earthquakes, stalked by vultures, bloodied by bombs.

Children are always innocent, and so they are compelling subjects when a war or political situation is complicated. They are also not quite fully vested members of society, which makes it somehow more acceptable to exploit their images. In Nick Ut’s 1972 photograph of a girl fleeing a napalm attack in Vietnam, the child is naked, which would not be incidental to the image if the victim was an adult. The children in the Syrian videos are held and manipulated by older hands, pulling at the flesh around their glassy eyes; the impact of this medical objectification would be even more horrifying if they were adults.

For some reason — perhaps because they are in our care, we instinctively believe they belong to us — it doesn’t seem quite as invasive of a child’s privacy to picture her covered in blood and crying, as Getty Images photographer Chris Hondros did in 2005 in Iraq, when he photographed 5-year-old Samar Hassan after American soldiers shot up her family’s car, killing both her parents.

But these images are often so deeply emotional and volatile that their power is ephemeral. One famous 1904 photograph of a man from Congo mourning his child is particularly poignant. He is seen in profile, sitting on a low ledge, contemplating a small, severed hand and foot, all that remains of his daughter after she was killed, dismembered and cannibalized by armed agents of a Belgian rubber company. It was a powerful image, disseminated by missionaries who sought to indict the colonial regime of King Leopold II of Belgium. Today it seems melodramatic.

The power of Ut’s horrifying photograph of Kim Phuc screaming as she runs down a Vietnamese road is undiminished. But the image has become so famous that it is compartmentalized in the category of “icon,” felt as a powerful aesthetic object but disconnected from the history — from the American napalm — it contains. Four decades later, it reads like a scene from a pageant of generic historical horrors, not a document of a particular war and a particular atrocity.

We often credit images such as Ut’s with changing the course of public opinion. But his photograph came late in the American people’s reassessment of Vietnam, with the Paris peace talks already underway. Images of suffering don’t necessarily forge popular attitudes ex nihilo; they catalyze an already gathering consensus.

Images of dead children are so excruciating that we are now well-trained to short-circuit our emotional responses, to move from horror to suspicion to indifference. The suffering of Israeli and Palestinian children is so fraught that it’s tempting not to look. The debate over who owned the bomb that killed BBC journalist Jehad Mashhrawi’s 11-month-old son — the Israelis or the Palestinians — neutered the impact of one of the most powerful images of 2012. That photo, and the controversy surrounding it, demonstrate why a foreign policy based on reaction to powerful images would be dangerous, inconsistent and probably hypocritical.

Concern over the failure of images to elicit compassion has been around for decades, at least. Susan Sontag articulated it best in her 1977 book “On Photography,” which called for an “ecology of images” — a more sustainable way to remain connected to their power and meaning. The surfeit of photographs, their superabundance, their abuse and numbing effect can deaden and corrupt us: “Images transfix. Images anesthetize.”

We are all forced, in private ways, to create a personal ecology of images. We choose to look, we bear as much as we can, yet we often turn away in anger or annoyance when an image seems to demand too much of us. Images of suffering children, in particular, are subject to a kind of emotional inflation, losing power if used too often or without regard to how we can channel the feelings they invoke. Shortly after Eisenstein’s mother holds up the body of her son, the filmmaker repeats the trope, upping the emotional stakes, with what is one of the most famous scenes in the history of cinema: A baby carriage teeters on the stairs, then careens down them. Extreme images of suffering are self-deflating; after you’ve used one, the only option is repetition, intensification, an increase in volume. They lead only to more passion, not understanding.

If photographs help build collective outrage about violence, war, colonialism and genocide, they may also be helping to dismantle international norms. The one consistent fact about the horrifying images that have come out of Syria over the past 21 / 2 years is that in many cases, we don’t know who made them and what they depict. All we see are decontextualized cruelty and misery. Cynicism creeps in, and there is a natural tendency to push the images away as a kind of insoluble puzzle.

Our own government has exacerbated this photographic and moral crisis. The Iraq war was sold to the American people in part with carefully annotated satellite photos that purported to show evidence of weapons of mass destruction. Those images were misread or misrepresented, and when their verity dissolved, perhaps some of our fear of such weapons dissolved with it, too. When torture, as morally reprehensible as the use of chemical weapons, became official U.S. policy, cloaked in euphemisms about “enhanced interrogation” and “stress positions,” another red line was crossed in our understanding of international norms. Media organizations, including The Washington Post, kept many of the worst torture images from Abu Ghraib out of wide circulation, and the few that did make it through the rigors of self-censorship, we were assured, confirmed only some surreal, Gothic anomaly. Torture looked like late-night frat games, not a deadly policy of abuse.

So it is little wonder that Americans are uninterested in engaging with images of suffering children in Syria and unconcerned about the introduction of chemical weapons into the Syrian conflict. Long after she called for an ecology of images, Sontag despaired of the idea. “There isn’t going to be an ecology of images,” she wrote in “Regarding the Pain of Others.” There is no way “to ration horror, to keep fresh its ability to shock. And the horrors themselves are not going to abate.”

That is where we are now, in an ecosystem of images and an ecosystem of international decency that have been irremediably polluted.

Also in this week’s Outlook section: Author and filmmaker Sebastian Junger says sometimes being anti-war requires embracing force, Syrian novelist Samar Yazbek says she’s divided on questions facing her country, Eliot Cohen debunks five myths about cruise missiles and William Dobson reviews a book on how presidents go to war. Read more from Outlook, friend us on Facebook, and follow us on Twitter.