A vehicular imaging system includes a forward facing photosensor array and a control responsive to the photosensor array. The control processes an image data set indicative of captured images, and the control processes a reduced image data set of the image data set to determine whether an object of interest is within a target zone of the captured image. The reduced image data set is representative of a portion of the captured images as captured by a particular grouping of the photosensor elements. The control adjusts the reduced image data set so as to be representative of a portion of the captured images as captured by a different particular grouping of the photosensor elements, and adjusts the reduced image data set in response to a determination of a change in a focus of expansion of the captured images.