"We are already at the point where you can't tell the difference between deepfakes and the real thing," Professor Hao Li of the University of Southern California tells the BBC. We are at the computer scientist's deepfake installation at the World Economic Forum in Davos which gives a hint of what he means. Like other deepfake tools, his software creates computer-manipulated videos of people - often politicians or celebrities - that are designed to look real. Most often this involves "face swapping", whereby the face of a celebrity is overlaid onto the likeness of someone else. As I sit, a camera films my face and projects it onto a screen in front of me; my features are then digitally mapped.

One video shows Barack Obama using an obscenity to refer to U.S. President Donald Trump. Another features a different former president, Richard Nixon, performing a comedy routine. But neither video is real: The first was created by filmmaker Jordan Peele, the second by Jigsaw, a technology incubator within Alphabet, Inc. Both are examples of deepfakes, videos or audios that use artificial intelligence to make someone appear to do or say something they didn't. The technology is a few years old and getting better.

As is the case with many technological developments, 'deepfakes' -- videos in which someone who did not originally appear in the clip is rendered into it using artificial intelligence (AI) -- largely started in the world of pornography. Viewers, should they so desire, can now watch videos of their favourite musicians and film stars "in action," although that celebrity was never in that video. In these cases, increasingly sophisticated tools are used to put the musicians and film stars' faces onto pre-existing pornographic videos. There can obviously be a sinister, non-celebrity side to this too. The recent Sam Bourne novel, To Kill The Truth, features a protagonist Maggie Costello who appears in such a video as part of a cruel plot to undermine her.

San Francisco (CNN)Deepfake videos are quickly becoming a problem, but there has been much debate about just how big the problem really is. One company is now trying to put a number on it. There are at least 14,678 deepfake videos -- and counting -- on the internet, according to a recent tally by a startup that builds technology to spot this kind of AI-manipulated content. And nearly all of them are porn. The number of deepfake videos is 84% higher than it was last December when Amsterdam-based Deeptrace found 7,964 deepfake videos during its first online count.

In November 2017, a Reddit account called deepfakes posted pornographic clips made with software that pasted the faces of Hollywood actresses over those of the real performers. Nearly two years later, deepfake is a generic noun for video manipulated or fabricated with artificial intelligence software. The technique has drawn laughs on YouTube, along with concern from lawmakers fearful of political disinformation. Yet a new report that tracked the deepfakes circulating online finds they mostly remain true to their salacious roots. Startup Deeptrace took a kind of deepfake census during June and July to inform its work on detection tools it hopes to sell to news organizations and online platforms.

While Americans celebrated a long Labor Day weekend, millions of people in China enrolled in a giant experiment in the future of fake video. An app called Zao that can swap a person's face into movie and TV clips, including from Game of Thrones, went viral on Apple's Chinese app store. The app is popular because making and sharing such clips is fun, but some Western observers' thoughts turned to something more sinister. Zao's viral moment was quickly connected with the idea that US politicians are vulnerable to deepfakes, video or audio fabricated using artificial intelligence to show a person doing or saying something they did not do or say. That threat has been promoted by US lawmakers themselves, including at a recent House Intelligence Committee hearing on deepfakes.