1. An image processing device comprising: facial region extraction means for extracting a facial region including a face, after detecting the face pictured in an image; identification information acquisition means for acquiring identification information for identifying a face in the facial region extracted by the facial region extraction means; first integrated processing means for performing integrated processing by determining if a face being tracked and a face pictured in an image to be stored in a predetermined storage period after vanishing from the image are the face of the same person based on the identification information; and second integrated processing means for performing integrated processing by determining if a face being tracked and a face pictured in an image to be stored in a predetermined storage period after vanishing from the image are the face of the same person based on the identification information in a different manner from that of the first integrated processing means, wherein the first integrated processing means determines a threshold value on the basis of a relationship between an estimated area in which the stored face image is predicted to appear and a position of the face being tracked, calculates a similarity between the face being tracked and the stored face image, and determines if the face being tracked and the stored face image are the face of the same person based on the calculated similarity, and the threshold value corresponding to the stored face image used in calculating the similarity, and the second integrated processing means calculates a similarity between the face being tracked and the stored face image with a plurality of face directions, and determines if the face being tracked and the stored face image are the face of the same person based on the calculated similarity for the plurality of face directions.