In an image sensing system where a camera apparatus and a client device are connected for controlling the camera apparatus by the client device, the client device displays and arbitrarily shifts a predetermined size of detection area in an object image sensed by the camera apparatus, enabling to quickly perform camera parameter control, such as focus adjustment or the like, based on image signals of the detection area, with a small amount of transferring data. Moreover, detection areas of a sensed image are synthesized by controlling camera parameters for each of the detection areas so as to optimize camera parameters for all of the areas in the object image.