1. A method of generating discriminant functions for distinguishing obscene videos using visual features of video data, comprising: (a) creating a first frame set by extracting a predetermined number of frames for each video data unit from a group of video data units classified as obscene or non-obscene, and creating a second frame set by selecting the frames; (b) generating a frame based discriminant function by extracting visual features of frames of the second frame set, and then generating a first discriminant value by determining whether each frame of the first frame set contains obscene video data; (c) generating a group frame based discriminant function by extracting visual features of a group of frames of the first frame set, and then generating a second discriminant value by determining whether the frames of the group contain obscene video data; and (d) generating a synthetic discriminant function by using the first and second discriminant values as a representative value of the video data.