1. An information processing system for calculating an image taking position of each of a plurality of images, the information processing system comprising: memory; and a processor communicatively coupled to the memory, wherein the processor comprises: a storage unit for storing thereinto a selected image set comprising images whose image taking position has been calculated, the images being selected from among the plurality of images; a calculation unit for calculating a plurality of image taking position candidates for an unselected image of the plurality of images, on a basis of correspondence points in the image with the images included in the selected image set; a selection unit for selecting an optimum image taking position having a highest degree of coincidence in correspondence points, from among the plurality of image taking position candidates for the unselected image; a determination unit for determining whether or not the unselected image is added to the selected image set, on a basis of the degree of coincidence at the optimum image taking position and the degree of coincidence at another image taking position candidate; and a reconstruction unit for reconstructing a three-dimensional shape of an image taking target on a basis of the images included in the selected image set and the respective image taking positions thereof.