1. A monitoring method, implemented by a monitor configured to brake a vehicle, the monitor comprising a microprocessor mounted in the vehicle and a stereo camera, comprising: detecting, in the monitor, an obstacle using an image formed by the stereo camera and including depth information; setting, in the monitor, a preset region around the detected obstacle as an interest region; detecting, in the monitor, an interest object present in the interest region, wherein the detecting of the interest object includes: detecting feature points from the image; and detecting the interest object in the interest region using the feature points; and tracking, in the monitor, the detected interest object, wherein in the detecting of the feature points, a threshold for detecting the feature points in the interest region is set to be lower than that in regions other than the interest region.