The software is based on face-swapping algorithms. A deep-learning neural network is trained to identify someone's face in a still video frame – such as an adult actress in a blue movie – and swap it with someone else's face – such as a TV celeb or singer. Repeat this at 30 or 60 frames per second, and you've got an AI-doctored video.
For example, in this safe-for-work video, the app has pasted Star Wars actress Daisy Ridley onto someone else's body.
But it's not super easy (yet):
The process to create these incredibly damaging faked videos is, thankfully, not trivial, but not impossible. You need the software – a desktop program dubbed FakeApp – plus a big batch of photos of your victim to train the application's deep-learning neural network, the video to paste the face onto, and a little tweaking here and there to render the output believable.
It's not all prurient, of course. Here is a video where someone replaced Angela Merkel's face with Trump's.