Human image synthesis can be applied to make believable and even photo realistic renditions of real humans, moving or still.
A synthesized human image is constructed by first sampling the target by means of 3D scanning and photography and creating a 3D model based on the samples, applying statistical information and approximations. Synthesis with an actor and suitable algorithms is applied using powerful computers. The actor's part in the synthesis is to take care of mimicking human expressions in still picture synthesizing and also human movement in motion picture synthesizing. Algorithms are needed to simulate laws of physics and physiology and to map the model and its appearance and movements accordingly.
Documentation of human image synthesis in action
Many films using Computer generated imagery have featured synthetic images of humans or human-like characters. The Matrix Revolutions bonus DVD documents and depicts the process in some detail and the techniques used, including facial and limbal motion capture, and projection onto human models.