1. An apparatus for extracting spatio-temporal feature and detecting video copy based on the same in a broadcasting communication system, comprising: an original video feature extractor configured to receive an original video and extract spatio-temporal feature of the original video, the original video feature extractor comprising: a unit configured to divide a frame of the original video into a plurality of blocks and calculate an average luminance value F(t,i) of each block, wherein F(t,i) is an average luminance value of an i th block of a t th frame; a unit configured to generate a weighted average luminance value F w (t,i) of the frame by applying a spatial weight to the average luminance value in accordance to F w ⁡ ( t , i ) = ∑ i = 1 N ⁢ w ⁡ ( i ) ⁢ F ⁡ ( t , i ) wherein w(i) is the spatial weight assigned to the i th block, and N is a number corresponding to all of the blocks in the frame; a unit configured to generate a differential luminance difference Δ′(t) of the frame by computing a difference between the weighted average luminance values of a previous frame Δ w (t−1) and a current frame Δ w (t) in accordance to Δ′(t)=Δ w (t)−Δ w (t−1) wherein Δ w ⁡ ( t ) = ∑ i = 1 N ⁢ w ⁡ ( i ) ⁢ Δ ⁡ ( t , i ) in which Δ(t,i) corresponds to a difference between an average luminance of an i th block of t th frame and the average luminance of the i th block of the (t−1) th frame and is expressed as Δ ⁡ ( t , i ) =  F ⁡ ( t , i ) - F ⁡ ( t - 1 , i )  ; a unit configured to select the frame having abrupt luminance change when a local threshold is applied to the differential luminance difference Δ′(t) of the frame, as a keyframe of the original video; and a unit configured to calculate spatio-temporal feature of the original video based on temporal and spatial characteristics of the keyframe; an original video feature database configured to store the extracted feature; a query video feature extractor configured to receive a query video and extract spatio-temporal feature of the query video; and a feature comparison and decision unit configured to compare the spatio-temporal feature of the original video and the spatio-temporal feature of the query video and decide similarity of the original video and the query video based on the spatio-temporal features of the original video and the query video.