1. An electronic system comprising: an image-sensing device comprising an image-sensing area that generates a picture comprising a noisy region; and a processor coupled with the image-sensing device, configured to select a tracking region from the portion of the picture outside the noisy region, wherein the tracking region corresponds to an operative region of the image-sensing area, wherein the tracking region is an intersection region of a first region and a second region, wherein the first region comprises a plurality of successive rows of pixels, which do not include any pixel of the noisy region, and the second region comprises a plurality of successive columns of pixels, which do not include any pixel of the noisy region.