1. An image-processing device configured to process image data including at least one face image, the image-processing device comprising: image-input means configured to input the image data; face-detection means configured to detect the at least one face image from an image frame of the input image data; importance-determination means configured to determine importance of each of the at least one detected face image; and priority-determination means configured to determine priority of each of the at least one detected face image based on the determined importance, wherein the importance-determination means determines the importance considering data on a size and a position of the detected face image shown in the image frame, and a priority determined by last time by the priority-determination means.