In a basement at BBC TV Centre is a storeroom that houses 150,000 library tapes. These are used by reporters and producers compiling news reports and range from footage of specific incidents to general pictures of people doing everyday things.
The library houses thousands of tapes
They're often known as "wallpaper shots" but every now and then problems crop up over pictures that may on face value seem perfectly innocent.
For example, one couple were filmed simply walking in a park - they were aghast to see the pictures on TV as they were in hiding on a witness protection programme and were concerned the footage could give away their location.
In order to avoid repeating any offence, the BBC tries to track down every instance when those particular pictures have been used. That's no mean feat because as well as the 150,000 tapes in TV Centre, the full archive of film, video and audio tape stretches to millions of items.
So what can the BBC do to stop problems arising in the first place?
It's often impossible to ask everyone for permission
"If we're filming close-up pictures of people, the chances are we've asked permission and they've said yes," explained cameraman Duncan Stone.
"If we haven't got permission to film, we're just doing general shots of people in the streets, then if someone came up and said: 'Please don't film me', we would stop filming them or we wouldn't use that shot in the edit.
"There are many places where you have to be slightly delicate in the way that you film - in prisons or in hospitals for example. If I go into a hospital ward to start filming I would speak to the patients just to make sure they're happy with my presence whether they're happy with the camera being there.
"Then I would try to frame as much as I could the patients out of shot. So I would use backs of heads or close-ups of hands, so I wouldn't particularly identify those patients."
In fact, as well as issues of sensitivity and decency, there can be legal concerns as well. This is why the pictures used on stories about schools are often blurred or oddly framed.
Duncan Stone: Sometimes you have to be delicate
"If the headmaster has given us permission to film, he has sought that from the children and from their parents and we're OK to use those pictures for that story only," said Duncan Stone.
"But if we're doing a story about drugs or paedophilia or school bullying, we can't show the faces of schoolchildren and we can't start identifying the school. So we might use children's feet, we might show out-of-focus shots of children playing in the playground, using these techniques that don't identify the children and that school."
However, despite those precautions, for all sorts of reasons people do object to some pictures being used.
Pictures like this are used for a reason
"Imagine that we're filming at somebody's stag night or hen party and they've given us permission to use it in a report about the licensing laws," said senior complaints co-ordinator Lee Rogers.
"If we don't label that footage properly and it ends up being used in a different report, say about the dangers of binge drinking, those people might legitimately feel that we have misrepresented them in a negative way.
"Or if we filmed some stock footage of patients in a hospital and that footage is used in the future, it's quite possible that some of those patients may have passed away.
It's not difficult to imagine the distress their families would feel seeing their loved ones on screen without any warning in a story that had nothing to do with their case."
Lee Rogers: Pictures could get wrongly labelled
In such instances, there are steps that can be taken to stop the offending pictures being reused.
"We look back through all the records we have on our database and when we have established all the instances of that occurrence, we go to the shelves, we physically get that tape out and we mark it as Do Not Use," explained Nick Marcus, from the Information & Archives department. "We also alter the database where the records of these pictures are held.
"This is pretty effective but unfortunately because the BBC has so many outlets we can't always be sure we have captured every single instance of that shot. It may have been used 50 or 100 times and inevitably things do slip through the net.
Nick Marcus: Move to digital will help
"But we're gradually moving into a digital environment, where all stories and pictures are going to be stored on a computer and the beauty of that system is that if you mark a sequence Do Not Use once, it marks it for every subsequent occurrence so hopefully that should minimise the chances of this happening."