“Spoken words are supplemented with non-verbal visual cues to enhance the meaning of what we are saying, signify our emotional state, or provide feedback during a face-to-face conversation,” says Dr Barry-John Theobald, computing science prof at the University of East Anglia.
This kind of technology could be used to allow computers to implement highly realistic characters to communicate with people. For example, in the Star Trek episode The Return of the Archons, a computer presents itself as Landru.
(Landru from Return of the Archons [ST:TOS])
An earlier example is presented by Robert Heinlein in The Moon is a Harsh Mistress. The sentient computer MYCROFT creates a computer generated image of "Adam Selene" the imaginary leader of the lunar revolution.
...We waited in silence. Then screen showed neutral gray with a hint of scan lines. Went black again, then a faint light filled middle and congealed into cloudy areas light and dark, ellipsoid. Not a face, but suggestion of face that one sees in cloud patterns...
It cleared a little and reminded me of pictures alleged to be ectoplasm. A ghost of a face.
Suddenly firmed and we saw "Adam Selene."
Was a still picture of a mature man. No background, just a face as if trimmed out of a print...
Then he smiled, moving lips and jaw and touching tongue to lips, a quick gesture...
(Read more about Adam Selene)
I added the bold emphasis - pretty accurate description of what you're seeing in the first picture above from forty years ago, which is a still taken from a video.