1. An image processing device comprising: a processing unit; and a non-transitory computer-readable medium coupled to the processing unit storing instructions that, when executed by the processing unit, cause the device to: extract a facial region including a face, after detecting the face pictured in an image; acquire identification information for identifying a face associated with the extracted facial region; perform a first 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 perform a second 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, wherein the first integrated processing is performed by determining 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, calculating a similarity between the face being tracked and the stored face image, and determining 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 wherein the second integrated processing is performed by calculating a similarity between the face being tracked and the stored face image for a plurality of face directions, and determining 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.