[touchofevil]

I've worked in the visual effects industry for many years and this is incredibly interesting. In vfx to create a face replacement, we would have to create a 3D model of a head and then texture it with photos/scans of a the desired face. Then we would 3D track this cgi head onto an actor in the shot and then animate the face either by hand or using motion capture data from the stand-in actor's face. Then you'd light and render the cgi head and composite it into the shot.

This video shows the process: https://youtu.be/rsPq2qp_Z-E

And here's an article about it: https://www.fxguide.com/quicktakes/di4d-in-la/

It's pretty incredible that there's a completely different way to do a head swap. Of course, the vfx method gives the artist complete control over what the face/head does.