Ten years ago, the devastating Indian Ocean tsunami was to change the way the BBC handled emails and photos taken by members of the public, who found themselves, often unintentionally, at the centre of big news stories.
While the BBC had always encouraged audience participation, from reading out letters on the wireless to the early days of radio phone-ins, it was the tsunami on 26 December 2004 which led to a significant shift in the way we dealt with these contributions. Eyewitness accounts told the story where we did not have correspondents on the ground.
On that day, the BBC received thousands of mostly unsolicited emails from people who had been in Thailand, Sri Lanka, Indonesia and elsewhere when the tsunami had hit and had witnessed dreadful things. And then there were the emails from people who had been unable to contact loved ones.
'A very different story'
The BBC's user-generated content (UGC) hub came to life. Initially, it was for a three-month pilot, with three journalists from different areas of BBC News brought together to gather the best material sent in by the audience and share it across the BBC.
But just as the pilot's success was being evaluated, suicide bombers targeted London's transport network during the rush hour on 7 July 2005, killing 52 people. It was a moment which would demonstrate just how important and integral UGC had become to a breaking news story.
The BBC initially reported the police line that there had been power surges on the underground. But for those on the hub, the emails and text messages which soon began pouring in, were telling a very different story.
By piecing these emails together, a picture emerged of what was really going on and we knew the locations of all four devices by 09:58, just over an hour after the first bombs went off.
Some of the first emails into the BBC
Boris, London: Kings Cross was closed and evacuated between 08:50 and 09:00.
Joe, London: Arrived into Liverpool St at about 08:57 on overland train. Seemed like chaos. Police were evacuating the area because of an explosion. Police and Fire Brigade arriving on the scene
Andrew McCormack: My girlfriend works up by Holborn and has just called to tell me a bus has exploded outside her office in Tavistock Square, bodies strewn all over the road etc.
Peter Fuller, London: Someone has just arrived in the office who claimed to be on the tube train that was involved. He was on the Metropolitan line coming into Aldgate, there was a loud bang and a large flash, the train stopped and the lights went out. Smoke started coming into the carriage and people were screaming. He said there was a carriage that had been 'ripped apart like a tin can' and he could see people lying inside, there were several people bleeding with head injuries.
At 11.30 a photo from Alexander Chadwick landed in our inbox, one of the most iconic shots of a terrible day. This was to become the moment the hub's importance was cemented in the newsroom.
The photo was taken in the Piccadilly Line tunnel as commuters made their way to a station from the bombed train.
Three of the bombs went off underground. Unlike the attacks of 9/11, these happened out-of-sight of the news cameras. The only people who were there to witness it were commuters, tourists, people who just happened to be there. But many of them were armed with a camera phone.
We received more than 1,000 pictures and more than 20,000 emails. The main news bulletins were filled with this mobile phone footage from inside the tunnels.
The term citizen journalist became the label of choice to describe audience contributions. News organisations soon realised that if their audiences had been caught up in an event, they wanted to be able to share their experiences.
The BBC's UGC Hub became a central clearing-house for content. We collaborated closely with our colleagues at the BBC News website and those working on TV and radio as we all tried to encourage people to share their photos, texts and emails with us, helping us to illustrate our stories in the best way possible.
It's impossible to describe every event that the hub has been involved in over the last 10 years, but there are some that have significantly changed the way we worked.
Duty of care
On 11 December 2005, the Buncefield fuel depot in Hertfordshire exploded, giving rise to the UK's biggest peacetime blaze.
We received more than 6,500 emails containing pictures and video, including one from amateur film-makers Andy Dicker and Andy Ash. They had filmed the 200ft high flames from a field close by and sensibly moved away quickly when they realised one of the tanks still had the potential to explode.
Ever since then, we've always made it clear to contributors that they should not put themselves, or anyone else, in any danger in their bid to capture an event.
The Hub continues to rely on direct contact from those with a story to tell or content to share, via email, SMS or forms on our website stories. But our work has increasingly shifted to take in the masses of content being shared on the wider web, especially through social media including Facebook and Twitter, as well as YouTube.
For example, the BBC had no access to Burma to cover demonstrations there in 2007. Instead we were able to tell the story of the ultimately failed protests through the testimony of tourists using Facebook at internet cafes.
In 2009, there was a moment that further underlined the shifting landscape for newsrooms when an amazing image of a plane that made an emergency landing on the Hudson River in New York was initially shared with millions of people not via any news provider, but via Twitter.
Later the same year, protests in Iran - where foreign reporters again had restricted access - were covered mainly thanks to social media, which gave the protesters themselves, not tourists, a voice and a platform on which to speak to the global media.
Then came 2011 - what many consider to be a watershed year in this story. London and other cities exploded in riots, a huge tsunami hit Japan - and the so-called Arab Spring began. All of them huge news stories, affecting large numbers of people, who had the devices and software at their fingertips to record and share their experiences. However, that meant we had an even bigger job at hand...
Verification is one of the most important tasks that we do. We always check every image, video or key contact before we broadcast them, to make sure they are genuine and also to check any potential copyright issues.
UGC, social news and the BBC: James Harding, director of news and current affairs:
Citizen journalism is not just a competitor to established news media, but a streaming source of information and ideas for it.
And the internet has turned our audience into a giant fact-checking machine: journalists are more directly and immediately accountable; our viewers, listeners and readers do not need simply to throw a shoe at the TV or put their foot through the paper, they can promptly e-mail or tweet us to point out our mistakes. This can be embarrassing, no doubt, but surely makes it more likely we will get it right.
The BBC has a team dedicated solely to harvesting user-generated content and, in the short time I have been there, I have seen it transform the coverage of the Boston Marathon bombing, the street-fighting in Cairo, the political row over Tesco's and Next's employment practices, not to mention the recent weather.
Source: James Harding speech
Sometimes it's incredibly difficult to do that, particularly when contributors are hard to reach, or if getting in touch might put them in danger. In those cases we enlist other BBC colleagues who know the area and the story, to help identify them or use one of the many tools in our armoury to check the authenticity.
Acquiring and verifying UGC video became a lot more complicated and forensic during the Arab Spring. We had to be extra careful we were not being duped by propaganda and we developed several processes to make sure we are reporting fact and not old material or footage from a different event. This was tested in November 2014 when a video started being rapidly shared across social media, claiming to be of a "hero boy" in Syria.
There were too many doubts about it so the UGC hub advised outlets against running it. And we were correct. Days later it transpired that it was indeed a fake.
We continue to learn and try to keep pace with changes in technology and audience behaviour. New applications and tools are emerging all the time and we need to be aware of that.
We have technology on our side to help sift through the millions of messages that are posted every minute on various social media platforms.
This makes our jobs a little easier, but when 35,000 photos of winter snow drop into your inbox (which they did over two days in 2010), a human still needs to look at them and process them.