An image processing device comprises: an image string acquisition unit (200) which acquires an inputted image string which has a first through an nth image and a processing unit (100) which deletes a portion of the first through the nth images and carries out an image digest process. The processing unit (100) selects an sth image (where s is an integer which satisfies the formula 0≤s≤n+1) as a provisional digest image, selects a tth image (where t is an integer which satisfies the formula 0≤t≤s-1) as a provisional immediate prior digest image, selects a uth image (where u is an integer which satisfies the formula t
