The present invention makes a privacy protection area set on a video frame always match a masking block for the privacy protection area, thereby preventing video images taken from the privacy protection area from being exposed. One embodiment of the invention sets a masking zone corresponding to a privacy protection area on a taken video frame, keeps examining if the set masking zone does not match the privacy protection area, and adjusts the position of the masking zone on the video frame if it is determined that the masking zone does not match the privacy protection area, thereby preventing video signals taken from the initially set privacy protection area from being outputted.