What are deepfakes and why are they a concern?

Things do not appear as they seem on this year's Channel 4 alternative Christmas message. The broadcaster has decided to raise awareness of deepfake technology for 2020, showing a false depiction of the Queen. So what are deepfakes and why are they of concern? Deepfakes use ever-improving artificial intelligence and machine learning, allowing people to combine and superimpose existing images and videos of a person to make it look like they have said something they have not. While these can often be used as humour, they are also open to abuse by those aiming to deceive others, particularly in politics.