1. An image-processing system operative to process image data obtained by capturing images outside a periphery of a vehicle, the image-processing system comprising: a plurality of image-capturing units that is affixed to the vehicle and that generates image-data items by capturing images outside the periphery of the vehicle; a bird's-eye-view-image-drawing unit configured to generate a bird's-eye-view image by determining a viewpoint above the vehicle for each of the image-data items generated by the image-capturing units based on the image-data item so that end portions of real spaces corresponding to two adjacent bird's-eye-view images overlap each other; an image-composition unit configured to generate a bird's-eye-view-composite image by combining the bird's-eye-view images with one another according to a predetermined layout; an object-detection unit configured to detect at least one object existing in at least one real space corresponding to at least one joining portion where the bird's-eye-view images included in the bird's-eye-view-composite image are joined to each other; a border-width-setting unit configured to determine a border image based on the overlap portions of the bird's-eye-view images included in the bird's-eye-view-composite image, the overlap portions being included in the joining portion, and to change a width of the border image when the object-detection unit detects at least one object existing in a real space corresponding to the overlap portion; and an image-addition unit configured to generate a border-and-bird's-eye-view-composite image in the joining portion by superimposing a border image having a width set by the border-width-setting unit on the overlap portion of one of the bird's-eye-view images.