1. A method of estimating position and orientation of an image-capturing device comprising: (A) obtaining a preceding set of frames by using said image-capturing device; each said frame including a set of image data; (B) estimating a previous position and orientation of said image-capturing device by using said set of image data included in at least one said preceding frame; and (C) estimating a current position and orientation of said image-capturing device by replacing a set of image data included in said at least one preceding frame by a set of image data included in at least one subsequent frame; wherein said at least one subsequent frame is obtained by using said image-capturing device.