1. An image-processing apparatus that generates a combined image by performing blending of a plurality of images acquired in time series, the image-processing apparatus comprising: a discrete-motion-vector calculating portion that sets a plurality of discrete measurement regions in a standard image and a reference image that is acquired before the standard image or a combined image generated on the basis of the reference image, and that calculates motion vectors separately for the plurality of measurement regions and confidences of the motion vectors; a global-vector calculating portion that calculates, on the basis of the motion vectors and the confidences thereof calculated by the discrete-motion-vector calculating portion, a global vector that indicates a motion of the standard image as a whole and a confidence of the global vector; a local-vector interpolating portion that calculates, on the basis of the plurality of motion vectors calculated by the discrete-motion-vector calculating portion, a local vector of a processing target region in the standard image; a local-vector-confidence interpolating portion that calculates, on the basis of the confidences of the plurality of motion vectors calculated by the discrete-motion-vector calculating portion, a confidence of the local vector of the processing target region; a motion-vector selecting portion that selects one of the local vector and the global vector on the basis of at least one of the global vector, the global-vector confidence, the local vector, and the local-vector confidence; a motion-compensated-image generating portion that generates, on the basis of the vector selected by the motion-vector selecting portion, a motion-compensated image of the reference image or the combined image corresponding to the processing target region in the standard image; and a blending portion that performs weighted addition of the processing target region in the standard image and the motion-compensated image.