Warning: contains disturbing images

One sunny November afternoon last year, in a suburb of Los Angeles popular with street racers, a CCTV camera picked up footage of an eruption of smoke 100m down the road, first thin and white, then thick and black.

Moments later, a car pulled over by its source. A man got out, holding a camera. The film he took – shaking and swearing as it goes – records one minute and six seconds of the aftermath of a high speed car crash. There was no way for the filmmaker to know that inside the crumpled, flaming chassis was the actor Paul Walker, star of the Fast & Furious film series. The clip ends as the man runs to a safe distance down the pavement.

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More recordings exist. But it was these two videos that first showed up on the internet in the hours after 40-year-old Walker's death. By 6pm, gossip site TMZ had managed to get hold of the CCTV film, and put it online. The same day, whoever filmed the second clip uploaded it on to Facebook. From this point, news websites across the world – Mail Online, AOL, The Independent – hosted one or other video alongside their reports, as a riptide of sadness pushed Paul Walker to the top of Google's most searched terms. Here was a newly evolving dilemma for internet users. If film was being shown on TV news, armchair viewers would have had little choice but to watch. But they weren't, at least on British TV channels, and so there was a choice. You could view the final moments of Paul Walker's life. Or you could not. Click or not click.

It's impossible to gauge how many landed on either side. Among the tributes and 'RIPs' on comment sections, however, there were hints of discontent. "I'm sickened by the fact that this has been posted. I haven't watched it & can't understand why any1 would want to"; "It literally took me 10 minutes to decide to watch this"; "TMZ will post anything". Neither video clearly depicts either Paul Walker's death, or that of his friend Roger Rodas, who was driving. The negative reaction which bubbled up appeared to spring as much from outraged morality as queasiness. When do you have the right to watch someone die? Do you need a better reason than curiosity? Would I want strangers watching me?

Thirty years ago, television editors would have inserted themselves between the British public and those questions. If it were still up to the BBC, there'd be no occasion to ask them. "The depiction of death is, of course, a major intrusion on privacy justified only rarely by the public interest," says David Jordan, director of editorial policy and standards at the BBC. It might, however, broadcast footage from the outskirts of a fatality. "Showing the aftermath of violence allows the implications to be demonstrated without the offence."

But with the spread of video recording technology (seven in 10 people in the UK own a smartphone, according to Deloitte) and the rise of user-generated video sites such as YouTube, the responsibility for death censorship has shifted away from overseeing bodies towards regular people. The British Board of Film Classification – once Hydra-like in defence of public morality – is this month trialling a user generated content tool, which gently asks video-uploaders to age-rate their own clips. Power lies with the little man.

So much so, in fact, that if you had an ounce of desire for it, you could have got much closer to the scene of Paul Walker's death. On 1 December, the morning after, users of the findadeath.com forum – known as 'death hags' – had tracked down and shared pictures that would rarely appear on a mainstream news site: of a charred foot, a burnt body. "I feel for the daughter," commented a forum user going by the name 'kajerayn'. "There's no way she's not going to see the videos and pics. That's one thing that supremely sucks about the internet. Yes we have immediate access to everything, but on the other hand, we have immediate access to everything."

22 November, 1963. Almost exactly half a century before Paul Walker's Porsche GT was videoed hurtling into a pole, Abraham Zapruder, a dressmaker from Dallas, was setting up his 8mm cine-camera on a good vantage point. At 12.30pm, he would record the most viewed piece of death footage in history, capturing the moment John F Kennedy is shot in the neck, then in the head. A grainy hue on the film softens some of its shock-value. So, too, a sense that this records history, not murder. All the same – HD, or not – it was the first time I (and many others, I expect) saw a real person's head explode. One second the President is waving, sitting in the back of his open-top limousine, then something goes wrong, another shot is fired, and a fountain of blood erupts from Kennedy's head. A four-inch flap of skin falls over his eyes; Jackie Kennedy is crawling in panic over the boot as the clip ends.

How to handle film both newsworthy and graphic in the extreme? Various iterations of Zapruder's film have now been viewed millions of times on YouTube, but it was 12 years after JFK's death before the public need-to-know overcame taste considerations and a 1975 episode of Goodnight America broadcast the footage in full. Of the 32 cameras trained on JFK's motorcade on that day, Zapruder's was unique in catching the headshot. The amateur cameraman was horrified. He had a nightmare of Times Square lit up with the words 'See the President's head explode!' and insisted that LIFE magazine, to whom he sold the film for $50,000, exclude the most gory frame from its report. The publisher of LIFE also purchased rights to the motion picture, partly to protect the scoop, but also, he claimed, to prevent it from ever being shown in public.

For most of the 7,000 members of the Find a Death forum, the Zapruder tape is old news, a worn-out textbook. Instead, what keeps hags like 'Seagorath' awake at night is a piece of footage, recorded in 1974, which remains hidden to this day. "The Christine Chubbuck suicide is the holy grail of American death-hag footage," Seagorath explains to me in an email.

By 1974, the public was better accustomed to blood on TV. Vietnam had been beamed into wood-framed sets in US living rooms, and news cameras hadn't flinched as police beat seven shades out of black men and women protesting for civil rights. Wherever fatalities occurred, reporters were scrambling them in to segments on salacious TV news channels. Christine Chubbuck, a young broadcast reporter for one such channel, WXLT-TV, complained to her news director one day when a story of hers was cut to cover a racier shoot-out. Three days later, on 15 July, 1974, she was reading out the news when a technical fault jammed film of another gunfight in a local restaurant. Chubbuck rolled on seamlessly. "In keeping with Channel 40's policy of bringing you the latest in 'blood and guts'," she declared, "you are going to see another first – attempted suicide." Cameras still rolling, the reporter then drew a revolver and shot herself through the head. She had previously told her parents she was suffering from depression.

It's unlikely that the footage was recorded by home viewers. VCRs were yet to gain mass-market traction. Nothing has since emerged. Find a Death can't locate it, nor other death-hag haunts, Documenting Reality and BestGore. "The profound lack of Christine Chubbuck media footage is quite astonishing," says Seagorath, something he finds "tantalising and evocative". For the family of Chubbuck, the relative scarcity of recording equipment must provoke different emotions. They took out an injunction against WXLT-TV at the time, which prevented the channel from releasing any video. The family was given one copy, and supposedly the Federal Communications Commission (FCC) another. Users of Find a Death report shamefacedly that forum members have been in touch with Greg Chubbuck, Christine's brother, in an attempt to finagle access to their "holy grail". "It's the public's right to know," says user 'Seagorath', who feels no shame for his curiosity. "I hope they uncover it someday... Maybe Chrissy [sic] was trying to tell us something."

A particular sort of curmudgeon likes to blame the internet for creating fetish out of thin air. True perversion was birthed with YouPorn, they fear, blind to gleeful coitus carved on cave walls. There is a temptation, here, to imagine that fascination with dying is also something novel, spawned from the union of high-speed broadband, sinister forums and file-sharing sites. This is like cutting the head off a flower, and protesting that it came like that. What you could more accurately say is that UK society has, on the whole, decided that death is no longer a spectator sport – but at the same time has furnished those who still wish to look with an extremely easy means of doing so.

In 1777, when forger Dr Dodd was sentenced to death by hanging, 100,000 Londoners turned out to watch him drop; masses more than dirtied their shoes in the Spa Field Riots (1817), or Peterloo (1819). Tight-buttoned commentators worried that scaffold crowds were missing the point. In 1787, Francis Goze reported that hangings had "the appearance of a fair or merry-making, [which] tends to greatly defeat the end of punishment". In 1840, 28 years before the final public hanging in Britain, Dickens lamented that these crowds showed "no sorrow, no salutary terror, no abhorrence, no seriousness, nothing but ribaldry, debauchery and levity". (In A Tale of Two Cities, 1859, he would weave one of the most serious and sorrowful scenes in Victorian literature around an execution.) Progress to the 1960s, when only soldiers and doctors were likely to see a stranger die, and gory 'mondo' documentaries – pseudo educational exploitation films on taboo topics – could be procured through surreptitious channels. A number of 'mondo' filmmakers lugged tripods and equipment out to Africa, where it was easier to find, instigate or stage bloodshed.

And yet the internet has brought death film to a fresh peak of accessibility. The Bergs were one of the first to experience the horror of knowing a family member's violent death was viewable online, without the power to control it. In 2004, aged 26, US businessman Nick Berg was captured in Iraq and beheaded by an Islamist militant group, who uploaded footage to the web. "I think I reacted more to that news than to the news of his death, and even the way he was killed. I fell to the ground when I heard it," says his father, Michael Berg, over email. Yet Michael believes the footage should be publicly available, to tell the full story, around which conspiracy theorists have long battled.

His daughter Sara, Nick's sister, disagrees. Ten years later, the video's availability, not on YouTube, but on more controversial sites such as LiveLeak, "feels the same as it always has: horrifying, disgusting, and sad. The availability of the video ... is a massive invasion of his privacy". There is no reason a stranger could give that would justify their watching it, says Sara. "None. At the time it happened, law enforcement officials needed to view it to obtain evidence for criminal prosecution purposes, but at this point, they have done that." On Find a Death, some users wish they could unsee the clip: "I watched Nick Berg's beheading," commented 'gemini33', "and have regretted it ever since."

The hope for people who want footage of a family member taken offline is that the two main sites to which people upload video, YouTube and Facebook, decide themselves to block or censor the content. Google, which owns YouTube, promises to "carefully review" any footage of death if a relative petitions for its removal through a webform, but warns: "Please note that we take public interest and newsworthiness into account".

When does "public interest" elbow aside a desire for privacy and respectful distance? Previously that decision was taken by journalists or regulators. Now the boundaries are increasingly being drawn in Silicon Valley. Four billion pieces of content are shared every day on Facebook, 2,400 hours of footage is uploaded to YouTube. "They [Facebook and Google] will be defining what newsworthy is on their own terms," says obscenity lawyer Myles Jackman. "It's quite possible to argue that anything is newsworthy if someone, somewhere, has an interest in it. Whether that interest is prurient is quite a different matter."

Saddam Hussein in 2006. Muammar Gaddafi in 2011. Two of the most newsworthy executions caught on film, and shared as proof that neither man – one hung, the other beaten, shot and stabbed – had swapped in a body double for his final act. Even here, though, a vulture-like glee in comment sections pointed to prurience driving views as much as catharsis. You could watch them die and die again. And where the propaganda value of these clips was exploited by political opponents, so, too, it served the militants in Baghdad who beheaded British civil engineer Kenneth Bigley in 2004, counting on the ghoulish virality of a video to spread their message.

Last october, the prurience of death film reached 10 Downing Street. With a battle-cry to clean up the internet at full volume, David Cameron decided that Facebook had its moral compass set wrong. A video posted on the site had come to the Prime Minister's attention, depicting drug cartel Los Zetas decapitating a Mexican woman in a pink vest (her identity remains unknown). In early summer, Facebook had quietly dropped its ban on sharing graphic violence. The site ought to reflect "the world we live in", guidelines proclaimed. But after a BBC report raised questions over the Zetas beheading, and Cameron tweeted that allowing such content was "irresponsible", Facebook eventually removed the video.

Set up as a portal for students to hook up, Facebook now finds itself in the unenviable position of arbiter of public morality. At times, its edicts can seem arbitrary. The site famously bans pictures of the female nipple, unless it is involved in politics (such as with the nude Femen protesters), or breastfeeding. Violence, on the other hand, can be shared (but not beheadings) so long as the context is condemnatory. Dickens noted the difficulty of prescribing how people respond to the sight of an execution in the 19th century, and the point remains. "How you can guarantee that everyone who views an image is critical of it," says Myles Jackman, "I don't know." You might find murder titillating and breasts utterly mundane.

One response is easier to predict. Each time a user reports an extremely graphic video, somebody paid by Facebook or Google has to watch it, to ascertain if it falls foul of the site's standards (a set of Facebook guidelines leaked in 2012 announced that "crushed heads, limbs are OK, as long as no insides are showing"). An invisible army filters out footage of necrophilia, paedophilia, rape and gore – at least from these two socially responsible websites. Facebook is said to outsource as much as a third of its moderation to poorer countries, paying a dollar an hour for freelancers to watch footage that one former employee, a Moroccan contracted through a Calfornian-based outsourcing firm, described in 2012 as "very upsetting – no one likes to see a human cut into pieces every day".

One click, two clicks beyond Facebook or YouTube and censors watch over you no longer, while any blood at all is considered 'newsworthy'. Footage of death is not illegal to view, so no reason past decency prevents sites hosting footage of ordinary, unremarkable people dying – or from selling ads alongside it. LiveLeak does so, Documenting Reality is ad-free but has an 'invite only' membership fee.

On the other hand, anyone who declares themselves over 18 can visit the thread R/WatchPeopleDie on the content sharing site Reddit, and spectate. 'Group of monks beaten to death', 'Porsche Cayenne runs over woman's head' and 'Woman's suicide' are among the videos listed. It has 26,000 subscribers. The reasons people press play often stem from thrill-seeking or curiosity, but can branch into perversion and, even, education. One Redditor, named Lady-Tree, tells me she watches to inure herself for a career as a forensic scientist. A moderator on Reddit's WTF ('What the Fuck') thread, which specialises in surprises, often gory, admits to extreme desensitisation. "People say [a video of death] made them cry or that they need to get off Reddit for a bit and I'm just like, 'Hmm, not everyone sees these types of videos often'," he says. The one piece of imagery that made him shut his laptop does not bear repeating.

Everyone calibrates their own sense of taboo in the internet's outback. I had planned to watch many more death films for this piece, but couldn't get past the first few seconds. Reading about it sent acid to my stomach, and the night after I did watch a minute of Faces of Death (1978), I dreamt of holding a baby in my arms as it choked and turned blue. That, of course, is just one response, and that of somebody extremely squeamish.

If footage is available and you can handle it, why not? Nobody will stop you. "It's each to their own to some extent," reflects Find a Death forum user 'Michael555', who at 22 has been a death hag for at least five years. "But in the past few years I've begun realising just how much of an impact this has on the family of the people who are in these video clips. I'm not saying I won't view them if they're available online, but it would be for the best if these pictures and videos disappeared off the internet"