1. An image processing system, comprising: an input device that receives setting of a landmark in first medical image data obtained by capturing a certain tissue of a subject, at a position corresponding to a specific tissue identifiable in one or a plurality of pieces of second medical image data, the first medical image data being medical image data in which the certain tissue is depicted and in which motion of the certain tissue is analyzable, and the one or the plurality of pieces of second medical image data (1) being obtained by capturing the certain tissue of the subject in one or a plurality of capturing directions, (2) corresponding to the respective capturing directions, and (3) being medical image data that visualizes the specific tissue and that is obtained by performing contrast enhanced radiography on the certain tissue or being medical image data obtained by capturing the specific tissue into which an instrument is inserted; output circuitry that outputs data including information of a position of the landmark in the first medical image data as output data; acquiring circuitry that receives the output data and acquires, based on the position corresponding to the specific tissue in the one or the plurality of pieces of second medical image data and based on a landmark projection position obtained by putting the position of the landmark read from the output data in a three-dimensional capturing space and by projecting the put position of the landmark onto the one or the plurality of pieces of second medical image data, three-dimensional position information of the landmark in a three-dimensional capturing space of the second medical image data; and a display that displays image data obtained by superimposing, on the second medical image data of the certain tissue, based on the three-dimensional position information of the landmark, the first medical image data or analysis image data, the analysis image data being generated by analyzing the first medical image data.