I) Motion Capture is a process used for animating 3D graphics. Compare the traditional process where the motion of a 3D graphics object is input manually by an animator with a mouse or keyboard; with motion capture, the motion of the 3D object is directly controlled by the motion of a physical object, for example a character walks or flails his arms when a person physically walks or flails his arms.

II) A connection between the Zoetrope, Rotoscoping, and Motion Capture; they are all methods for getting still images to move in a lifelike fashion, aka animation. in particular, they use physical objects to create their illusion of movement, rather than just flat images as with traditional animation or film.
The Zoetrope creates its motion with pictures on a spinning table or wheel.


With Rotoscoping, the drawn pictures are directly traced on top of live footage. Note that the finished pictures don't have to be exactly as in the live footage; a man can be traced over as an 9-foot tall blue alien instead, for example.


Similarly with Motion Capture, a man could be remade in 3D images as a giant robot, a penguin, or a walking pineapple.



III) An emphasis on using a person's direct motions and movements to animate 3D images can be seen with this video that talks about how the movie Avatar was made.


IV) Organic motion capture is the most recently developed method motion capture system. older systems relied on a setup of markers on the subject whose motion will be tracked; while it worked, it proved cumbersome and expensive. Organic motion capture does away with the markers or any kind of devices on the subject, instead using a different kind of specialized camera to track a subject's silhouette.


http://wwwcremers.in.tum.de/pub/pub/rosenhahn_ki06.pdf