1. An image processing method for detecting a target, the image processing method comprising: acquiring depth information of an image; creating a histogram on the depth information of the image; setting a critical value of the depth information for detecting a region of a detection object from the image; extracting a region of the detection object from the image by using the set critical value of the depth information; verifying whether the extracted region of the detection object corresponds to the target; and storing the extracted region of the detection object.