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 a plurality of cross-sectional images representing cross-sections taken at a plurality of given points along a predetermined composition axis in the original image, the image sending means sending the image data of the cross-sectional images more than one times such that the image data of a different cross-sectional image taken at a different point is sent each time, 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 applying predetermined image processing to the image data of the cross-sectional images, and the image processing system further comprises a controlling means, wherein the controlling means determines, based on a predetermined determination criterion using a result of the image processing applied by the image processing means to the image data of the cross-sectional images sent so far, whether it is possible to determine a result of the image processing for the image data of a cross-sectional image representing a cross-section taken at an arbitrary point along the composition axis in the original image based on the result of the image processing applied by the image processing means to the image data of the cross-sectional image sent so far, if it is determined to be possible to determine the result, the result of the image processing is determined for the image data of the cross-sectional image representing the cross-section taken at the arbitrary point, if it is determined to be impossible to determine the result, the controlling means determines image data of a next cross-sectional image to be processed by the image processing means to determine the result of the image processing, and the controlling means causes the image sending means to send the image data of the next cross-sectional image to be processed.