1. An image processing system comprising: an image storage device and an image processing device being connected to be able to communicate with each other via a network, wherein the image storage device comprises: an image database for storing image data of a three-dimensional or higher-dimensional original image representing a subject; and an image sending means for sending, to the image processing device, image data of cross-sectional images representing cross-sections taken at given points along a predetermined composition axis in the original image, the image processing device comprises: an image receiving means for receiving the image data of the cross-sectional images sent by the image sending means; and an image processing means for obtaining subject information about the subject for each of the image data of the cross-sectional images, and the image processing system further comprises a controlling means, wherein if a first piece of the subject information obtained by the image processing means from image data of a cross-sectional image representing a cross-section at a first point along the composition axis and a second piece of the subject information obtained by the image processing means from image data of a cross-sectional image representing a cross-section at a second point along the composition axis satisfy a predetermined relationship defined based on anatomical characteristics of the subject, the control means exerts control to determine the subject information in a cross-sectional image representing a cross-section at an arbitrary point between the first point and the second point along the composition axis based on at least one of the first piece of the subject information and the second piece of the subject information, and if the first piece of the subject information and the second piece of the subject information do not satisfy the predetermined relationship, the control means controls the image sending means to send, as image data to be processed by the image processing means, image data of a cross-sectional image representing a cross-section at a given point between the first point and the second point along the composition axis.