It's very advanced, the software turns every pixel of your screen into a miniature camera, sensing slight fluctuations in the quantum field to pick up a shadow of your appearance. This is then augmented at the server-side using artificial intelligent guesswork to re-create your image.
Warning: it can also suck up a little of your soul or life-force, but the benefit to me is that I gain immortality. So not all bad. Well, for me anyways ...