1. A reference image setting unit comprising: a sample frame extract unit which receives a plurality of image frames taken for a certain period of time from image data generated by photographing an object; and a reference frame extract unit which compares the plurality of image frames with one another based on distances between a center point and a plurality of characterizing points in each image frame, extracts the least shaken image frame from among the plurality of image frames according to a result of the comparison, and sets the extracted least shaken image frame as a reference image frame.