Photograph by Mario Anzuoni / Reuters

On a bad day, being online feels like having someone strap you down, jam an I.V. into your arm, and pump untested “Clockwork Orange” drugs into your blood: the shuddering, Wi-Fi high; the low, a silicon-and-lead drag. On a worse day, being online is like being in a casino: it’s too noisy, you’re surrounded by strangers—you can hear the jangle of their coins, nickels on metal, and snatches of their conversation, scratchy, incomprehensible. Pictures flicker past, like the reels on a slot machine: apple, bell, banana. Pull the one-armed bandit; point, click, scroll. Cherries, cherries, lemon. The pictures shimmer and vanish, except when they don’t, because sometimes, when you close your eyes, a picture lingers, unwanted and unerasable, coating the insides of your eyelids the way a daguerreotype’s mercury fumes coat a plate of silver with a sitter’s wraith.

This summer, there are three photographs I cannot delete from the album in my head: a nine-year-old girl in pink shorts, holding an Uzi at a firing range in Arizona; a police sniper perched on top of an armored tank in Ferguson, Missouri; and a black-masked terrorist in a desert, about to behead an American journalist. Gun, rifle, knife.

All three pictures are stills; two are screen grabs from videos recorded on cell phones and posted online. It is in the nature of photographs to haunt. Even Instagram can capture only what’s passed, the gone moment. The logo for Snapchat is a white ghost, sticking out his pink tongue: a smiley face, blowing a raspberry. I once visited a man in New Hampshire, a collector who had turned his garage into a museum for more than five thousand daguerreotypes, all portraits. He’d picked them up at yard sales. He had no idea who any of the sitters were, no names for five thousand faces of people loved only by the long dead. His garage was like a morgue crammed with unclaimed bodies, like the cloud of dust where crumpled old Facebook pages end their days.

Seven hundred million photographs and videos are shared on Snapchat every day. Every minute, another hundred hours of video are added to YouTube, and nearly thirty thousand photographs appear on Instagram. Facebook mounts four thousand photographs every second. “The miraculous is everywhere,” a Sprint ad for the iPhone promises. “We can share every second in data dressed as pixels, a billion roving photojournalists uploading the human experience, and it is spectacular.” And it is spectacular. But a billion roving photojournalists are uploading, too, the unending, unsparing collective misery of humanity.

The three pictures that got stuck in my head this summer don’t belong together. What’s going on in them is wildly different in scale and in kind, for one thing—accident, outrage, atrocity—and even picturing them alongside one another is a kind of devastation, a collapse of meaning. They’re together in my mind mainly because I saw them one after another while reading the Times online, and because, in each, someone is threatening to use a weapon in a world gone very wrong. Seconds after the frame that I can’t unsee, the girl lost control of the gun and killed the man standing next to her with a single shot to the head. Days before the sniper mounted the tank, a Ferguson policeman shot to death an unarmed man in the middle of the street, in the middle of the day. Moments after the journalist, James Foley, fell to his knees in a sea of sand, his hands tied behind his back, the man in the black mask cut off his head. And then the pictures were posted: uploaded and downloaded, loaded, a burden to be borne.

I know what I first felt when I saw each one, aside from sick: the urge—a gut instinct, a child’s fantasy, really—to leap into the picture, save everyone, and stop everything. Grab the gun from the girl, the rifle from the sniper, and the knife from the terrorist. I remember what I thought next: she is so small; the tank has just passed a McDonald’s; the desert looks as otherworldly as the moon. I remember what distracted me: my own nine-year-old has the same sneakers as that little girl; the traffic lights on the street in Ferguson were green, which is funny, as if the tanks were obeying the laws of the road; the terrorist looks like Snake Eyes, that ninja G.I. Joe. I remember what happened next: I picked up the Snake Eyes action figure that someone had left sitting on the edge of our kitchen table, missing a shoe, and thought about where American weapons go, and where they don’t, and what they do, and what they don’t.

In the flicker, the flutter, the shutter-speed, Twittering blink of an eye, these three pictures became top hits. Most Seen. For a trending moment, they focussed emotion, and some attention, on the Second Amendment and gun safety, on race relations and the new militarism, on American foreign policy and the nature of a caliphate. Words of vengeance, words of protest, and words of eulogy swirled around them like wind in a hurricane. The hurricane will pass, and that wind will die, and the pictures will be left as bare as trees, stripped. For now, the wind is still whipping. On Tuesday afternoon, the Islamic State in Iraq and al-Sham posted to YouTube a video of another beheading: the murder of the thirty-one-year-old American journalist Steven Sotloff. By Wednesday morning, the screen grab of Sotloff on his knees in that deadly desert was everywhere. His name was the trendiest term on Google. More than a million people had searched for it. They looked and looked.