1. An apparatus for tracking positions of parts of an object, the apparatus comprising: a feature extracting processor configured to: receive a training depth image comprising pixels and depth information of each of the pixels, extract a foreground depth image of an object comprising parts from the training depth image, the foreground depth image of the object comprising some of the pixels of the training depth image and corresponding depth information, extract patterns by storing differences between the depth information of each pixel of the foreground depth image of the object and the depth information of pixels surrounding the each pixel of the foreground depth image of the object as a vector, each of the surrounding pixels being in either the foreground depth image of the object or a portion of the training depth image outside the foreground depth image of the object, and each of the surrounding pixels being located at a predetermined distance in a radial direction from the each pixel, said predetermined distance being greater than 1 pixel, extract features for each pixel of the foreground depth image of the object by calculating a histogram based on a frequency of the extracted patterns, and generate a feature set for each of the parts of the object based on the extracted features; a classifier training processor configured to train a classifier to distinguish which of the parts of the object each pixel of the foreground depth image of the object belongs to using the feature set; and a position determining processor configured to identify a part of an input image object of an input depth image to which each pixel of the input image object corresponds using the trained classifier and features extracted from the input depth image, and determine three-dimensional position information of each part of the input image object.