It used to be said the camera never lies, but that was before computer graphics. Now, computer generated imagery, or CGI, is taking film a step further by bringing historical characters back to life on screen.
Hitler, Stalin, Roosevelt and Churchill have been brought back to life for a TV documentary.
The sculpted face of Hitler was superimposed on the actor's head
The challenge of realistically recreating these historical characters was given to Soho's Moving Picture Company by production firm Tiger Aspect for a forthcoming documentary.
But there were a lot of steps in recreating the historical figures says Jim Radford, creative head of 3D at the Moving Picture Company.
"First we chose actors whose physical features, in terms of the shape of their heads, resembled those of the historical characters.
"We took a plaster cast of their heads upon which a sculptor sculpted the face of our historical character.
"That combination was scanned into the computer.
He said that this face was then textured and shaded to match the skin tones of the actor playing that leader. This ensured that when the two were put together for the final shot it fitted and looked like the historical character.
After this, said Mr Radford, came work to ensure the composite gave the impression that it was the same person and not two different materials.
"Then we added the dialogue and the range of expressions that was needed for each shot.
"And once that was done, we transformed the contemporary live action footage into 1940s colour archive."
The finished documentary will be shown on the Discovery Channel.
Of course, we will never know what Hitler, Stalin, Roosevelt and Churchill would think if they could see their new virtual faces and how events were portrayed.
But one historian believes that although this kind of technology can be very appealing, the possibilities are also "quite appalling".
Kathleen Burk, professor of history at University College London, says: "If programme makers maintain the honesty of those who have already used [this technology] and the high standards, one has to accept it because it's there and you can't put the genie back in the bottle.
"But those who come after them can take this technology: they can use it for propaganda, they can use it to create a history they would like actually to have happened, because people are the outcomes of their history.
"You can't get around that, and if you convince people that certain things have happened, you can lead people in directions that otherwise they might not wish to go."
Charles Brand, director of history and specialist features at Tiger Aspect, insists the producers took appropriate steps to ensure historical accuracy and keep the production ethically sound.
He says: "I think we were incredibly responsible and I would hope as a programme maker, and as a company, we would always be responsible to historical events.
"But in this particular case, because we were recreating archive, and people who switched on in the middle of the programme might think it was real archive, we knew that we had to be very, very sure.
"Not only did we research the material very carefully over a number of months but we then got the leading historians on each of these figures, and this period of history, to go through the script, word by word, and tell us if there was anything they thought those characters would not have said.
"And they were entirely happy with it.
"I think clearly when you invent a new technique like this there are going to be bad ways of using it as well as good ways.
"You can argue that when the car was invented there were bad sides to that as well as good sides.
"I don't think that we as programme makers can be responsible for every single way people may use or misuse it in the future."
The crossing of any ethical boundaries by the advance of this technology also raises "potentially enormous" legal implications, according to barrister Tim Kevan.
"In the civil court you can imagine that celebrities are going to be suing over fake videos.
"I think that probably it will come up most in the criminal courts and the faking of evidence.
"For example you could have fake alibis. Someone could suddenly turn up in their friend's home videos. Companies could be producing this sort of thing.
"I think ultimately, and ironically, the difficulty will be that it will undermine confidence in the whole system."
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