1. An image-based hand detection apparatus, comprising: a hand image detection unit configured to detect a hand image corresponding to a shape of a hand clenched to form a fist from an image input from a camera; a feature point extraction unit configured to extract feature points from an area, having lower brightness than a reference value, in the hand image detected by the hand image detection unit; an image rotation unit configured to compare the feature points of the detected hand image with feature points of hand images stored in a hand image storage unit, and then rotate the detected hand image or the stored hand images; a matching unit configured to compare the detected hand image with the stored hand images and then generate a result of the comparison; and a hand shape recognition unit configured to, if at least one of the stored hand images is matched with the detected hand image as the result of the comparison by the matching unit, select the at least one of the stored hand images as a matching hand image, wherein the feature point extraction unit is further configured to extract the number of edges, locations of the edges, and angles of the edges as the feature points of the detected hand image, the edges corresponding to areas with lower brightness than the reference value in the detected hand image.