1. An image forming system comprising: a photographing sensor configured to capture an image of a physical object; a detector configured to use an object model to detect a region of the image that includes the physical object, wherein the object model is trained by an image of the physical object, wherein the image of the physical object is extracted from a difference image by use of at least one sub-window, wherein each difference image is either a positive or a negative image of the physical object, and wherein each difference image corresponds to a difference between a first image of the physical object and a second image of the physical object; a status parameter computing processor configured to compute status parameters, based on the region where the detected physical object exists in the image of the physical object, so as to enable the physical object to be in the central region of the image; a controller configured to receive the status parameters, and adjust the status of the image; a memory device configured to store the image of the physical object; a display configured to display the image of the physical object; and a sub-window processor configured to use at least one sub-window to extract the image of the physical object from the difference image, wherein the sub-window processor is configured to: create double windows by simultaneously varying width and height of two windows, in an adjustable scale according to the image scale; vary the width and height of the double windows, by using consistent zoom parameters, and slide the double windows on the image, so as to capture a wide-range hidden pattern according to the scale, wherein the double windows are slid relative to each other in a horizontal direction or in a vertical direction, in order to capture a wide-range hidden pattern.