1. An image processing device comprising: a storage unit; an image processing unit for processing an image to obtain a pixel matrix of the image; and a control unit, comprising: a pixel point setting module for obtaining a predetermined number of pixel points from the pixel matrix of the image from the image processing unit; a pixel point acquiring module for acquiring a pixel point from the predetermined number of pixel points; a neighborhood defining module for taking the acquired pixel point as a center and defining a neighborhood around the acquired pixel point; an evaluating module for evaluating whether the difference between the pixel value of the acquired pixel point and the pixel value of any adjacent pixel point within the neighborhood on a one-by-one basis is greater than a preset value, if the difference between the pixel value of the acquired pixel point and the pixel value of any adjacent pixel point within the neighborhood on a one-by-one basis is greater than the preset value, defining the pixel point as a boundary point of an object from the image, and evaluating whether the boundary point has been recorded in the storage unit; a recording module for recording the boundary point in the storage unit if the boundary point has not been recorded in the storage unit, and the pixel point acquiring module further for acquiring an adjacent pixel point of the boundary point according to a preset rule; and an outline output module for acquiring all recorded boundary points and defining an outline of the object composed of the all recorded boundary points when the boundary point has been recorded in the storage unit.