1. A method of extracting a shape sequence descriptor for content-based retrieval of an image sequence that expresses the motion of an object by a plurality of frames, the method comprising: converting image frames included in an image sequence to frames, in a quantity of n (natural number), including only the object that is separated from a background; extracting shape descriptors, in a quantity of n, corresponding to the frames, in a quantity of n, using the object; generating a shape sequence by aligning the shape descriptors, in a quantity of n, according to a temporal order; obtaining conversion coefficients having frequency information by frequency-converting the shape sequence along the time axis; and extracting a shape sequence descriptor using coefficients in a low frequency area among the conversion coefficients.