By Tom Heneghan

PARIS (Reuters) - The threshold for publishing gruesome images like those of Muammar Gaddafi's death is falling as the internet and social media make many of the editorial decisions that used to be left to a small group of professional journalists.

The shaky video footage of Gaddafi's last moments was such a dramatic end to Libya's months-long struggle against its former dictator that many television stations around the world rushed to broadcast much of what they received.

Newspapers followed up on Friday morning, some splashing graphic photos of the bloodied former Libyan leader across their front pages while others opted for pictures of victorious anti-Gaddafi troops or file shots of Gaddafi in his heyday.

Showing images of a person in the throes of death used to be a newsroom taboo, but even this is now giving way under the pressure of instant internet publishing and -- thanks to camera phones -- the increasing availability of strong news footage.

"Over the past 10 years, whatever your society's standards were, they're notching toward more gruesome images," said Kelly McBride, ethics expert at the Poynter Institute journalism training center in St Petersburg, Florida.

In many cases, she said, news organizations now deal mostly with the question of how to publish a graphic but newsworthy picture rather than whether they should run it at all.

"News editors are very aware that these images are available anyway," said Ivor Gaber, professor of political journalism at City University in London.

HISTORIC IMAGES

Steven Barrett, professor of communications at London's Westminster University, said there was no doubt the images would be used. "This was a momentous event in world history," he said. Showing it was "not just to boost ratings."

Showing the footage was especially important in Libya and the Middle East, since the lack of such photographic proof of Osama bin Laden's death prompted many people in the region to ask whether the al Qaeda leader had really been killed.

"I doubt the vast majority of Libyans, and possibly the populace in the region, will raise any objections to the images," said Hayat Alvi, professor of Middle East studies at the U.S. Naval War College in Newport, Rhode Island.

Many television stations in Europe and the United States prefaced their broadcast of the Gaddafi death videos with a clear warning that disturbing images were about to be shown.

The main stations in Spain and Belgium gave no warnings, while the German channel ZDF showed a few images in its main evening news broadcast and then said: "There are others we don't want to show -- it's a question of human dignity."

European and United States newspaper front pages on Friday morning showed even wider differences in the way the print media handled those images.

No major U.S. newspapers ran pictures of the dying Gaddafi on their front pages. Of the 424 newspapers surveyed by Newseum, a Washington journalism museum, only about two dozen had page one images of him near or after death.

By contrast, London's Daily Telegraph, Guardian and Sun splashed grim photos across their front pages. The Guardian website balanced that with an op-ed piece entitled "Even Muammar Gaddafi deserved a private death."

Milan's Corriere della Sera printed a photo of the dead Gaddafi, blood trickling down his bare chest. De Morgen in Brussels covered its tabloid front page with a shot of him in agony, near death, with the quote "the people love me."

German newspapers were more discreet than ZDF television, showing few bloody images of the former dictator. French front pages seemed evenly divided between discretion and disrespect.

Le Monde in Paris printed a small black-and-white photo on its second page of Gaddafi's half-naked corpse displayed in Misrata, while Madrid's El Pais displayed the same shot large and in full color on its front page.

RISING TOLERANCE FOR GRUESOME IMAGES

"Tolerance for gruesome images is going up because more people search for them on the internet than we would have expected," McBride said. "So when it's delivered to them by a publication, they don't have the same righteous indignation."

Still, she said, the main check on media from publishing shocking pictures is the backlash from their audiences.

"U.S. audiences have the least tolerance for graphic images," she said, despite the high level of violence they accept in entertainment films. "It's a weird paradox."

While all the media experts said editors had to consider a mix of factors when deciding whether to run an explicitly violent image, Barnett stressed the key factor in any ethical assessment was the editor's intent in publishing it.

"If it's just to gratify, to maximize shock and horror, it's unacceptable," he said.

McBride, who often gets urgent calls from editors on deadline asking for ethical advice, said she gives them a rough checklist of the issues to consider before publishing.

They should ask what the news value of the picture is, whether it will in any way harm to the publication's audience and whether the publication can find alternative material to publish with fewer ethical concerns.

"There is so much that changes from one story to the next that it's hard to write rules for how to treat these images," she said. "Newsrooms have to go through this questioning process and figure it out for themselves."

(Reporting By Tom Heneghan and Peter Apps)