1. A method for detecting a side of an object in an apparatus for detecting a side of an object within an image, comprising: analyzing, by a boundary line detector, an input image to search a detection target region in which a target object is included; detecting, by the boundary line detector, a boundary line between the target object and a ground within the detection target region; calculating, by a side determiner, a gradient for the boundary line; and analyzing, by the side determiner, an image within the detection target region on the basis of the gradient to determine that the entirety of the detection target region is a region of the side of the target object or to determine a separated region corresponding to the side of the target object in the detection target region.