The killings have been both deliberately lurid and strangely intimate. Designed for broadcast, they have helped the Islamic State militant group build a brand of violence that shocks with its extreme brutality, yet feels as close to viewers as the family images on their smartphones.
Broadcast specifically to frighten and manipulate, the Islamic State's flamboyant violence consumes the world's attention while more familiar threats, like the Syrian government's barrel bombs, kill far more people but rarely provoke widespread outrage.
A few human rights advocates and anti-government activists in Syria are trying to reciprocate, creating shocking if nonviolent images and videos - even herding children in orange jumpsuits into a cage - to call attention to the wider scope of violence. So far, though, their voices have hardly been heard.
Cameras zoom in as captors lay hands on their captives - Western reporters, a Jordanian pilot, Egyptian Christian laborers. In the group's latest video, black-clad men lead the Egyptians almost gently, one by one, down a sunset-tinged beach, then saw off their heads until the waves turn red.
For many in the Middle East who obsessively share the latest images, the Islamic State's exhibitionist brutality is the apotheosis of several years of carnage gone viral. The group's bloody imagery, flooding social media already widely used to chronicle conflict, makes violence seem ubiquitous, even mesmerizing, and spurs a sensory overload that can both provoke feelings and numb them.
"It's like action movies," said Ahmad, 39, an employee of the Damascus Opera House in the Syrian capital, who asked to be identified by only his first name for his safety. Islamic State violence is stylized, as if in a Quentin Tarantino film, he said, in a macabre bid "to win the prestige of horror."
The killings have been answered quickly with airstrikes - from the United States, Jordan and, on Monday, from Egypt, which said it struck in Libya, where the Egyptian Copts were killed.
While the Islamic State's provocations draw pronounced reactions, however, the less-choreographed slaughter that has killed, for instance, more than 200,000 Syrians, fades to the background. Those bearing the brunt of the Syrian war's spillover across the region, and humanitarian workers trying to assist, frequently express anguish that government barrel bombings, the displacement of more than a third of the population and the gutting of the health care system do not bring similar attention - let alone dramatic action.
Of course, that is partly a matter of realpolitik. While Western governments decry Syria's president, Bashar Assad, for his indiscriminate attacks on civilians, they do not view him as a threat on the order of the Islamic State, which is encouraging followers to launch lone-wolf attacks in the West.
And it is partly because shock videos work. Even in Saudi Arabia, where beheadings are the state's method of capital punishment, they are not broadcast. When images of a recent execution leaked, they created a scandal.
But it is also because the shelling of cities in Syria has become almost numbingly normal. It is as if the value of trauma and shock has undergone a hyperinflation that neuters all but the most exaggerated visual representations of violence.
That, in turn, has pushed human rights advocates and activists to search for eye-grabbing images of their own.
Baraa Abdulrahman, an anti-government activist in the Damascus suburb of Douma, desperate to direct the world's attention to government airstrikes that were killing scores of people, set up a scene that echoed the Islamic State video in which the caged Jordanian pilot, in an orange jumpsuit, was burned alive.
He ordered an iron cage from a blacksmith and placed it against a backdrop of collapsed buildings, and then filled it with a gaggle of neighborhood children dressed in orange clothing. As the camera rolled, he waved a burning torch, asking why the world responded to the killing of the pilot but not to the deaths of children in Douma. Some of the children in the cage, he admitted, were frightened and cried.
"I'm very sorry to get to this point, to use the kids," said Abdulrahman, who uses a nom de guerre for security reasons. "But this is the fact. Our kids are getting killed every day, every moment, getting under the wreckage."
Yet images of mangled children no longer get traction, he said. "These sights, people now are used to them."
Anti-government activists are not alone in trying to compete with the war's most lurid imagery. The Syrian government has made much of a video of an insurgent ripping the organs from a slain soldier and taking a bite. Humanitarian organizations are in the same position.
A group training volunteer civil defense workers has circulated a video of what it calls "the miracle baby," an infant named Mohammad who is seen being pulled from the rubble of an airstrike. Opposition groups have passed around videos from the captured cell phones of pro-government fighters and soldiers who have apparently filmed their own cruelty, like one of a militiaman stabbing an old man in the head.
The U.N. High Commission for Refugees widely circulated images of triplets born in a snowstorm in a refugee camp, only to lose their mother to complications from childbirth.
"There is personal tragedy of mammoth proportions happening every day by the thousands in individual lives that never get picked up by a media camera," said Ninette Kelley, the director of the refugee agency in Lebanon, where more than a million Syrians have fled.
"Refugees whose lives have been irrevocably damaged, people who die from cancers that but for the crisis would have been treated in Syria, these wounds are very real but not always as visible."
A few have even been tempted to fictionalize. Last year, for instance, a viral video of a Syrian boy saving a girl from sniper fire turned out to have been staged by a Norwegian film crew.
"One of the things about traumatic imagery is that it can numb us and render us passive and helpless," said Gavin Rees, the Europe director for the Dart Center for Journalism and Trauma. "That is part of the gain for those who are producing these videos: They want to inspire fear and helplessness."