1. A photographing method, comprising: photographing an object; displaying the photographed object; calculating a real size of the object; generating grid lines for a user to estimate the real size of the object based on the calculated real size of the object; displaying the grid lines to be overlap to the photographed object; and adjusting a gap between the grid lines if the user changes the size of the displayed object with a zoom operation, wherein the grid lines include grid dots where two grid lines intersect, and one of the grid dots on the grid lines is displayed at a focus point.