1. A method for determining whether a first medical image and a second medical image are medical images of a same patient, comprising: selecting a first region in the first medical image; selecting a second region in the second medical image; determining a region common to the first region and the second region based on a boundary of the first region and a boundary of the second region; calculating a correlation coefficient based on image data from the first medical image in the common region and image data from the second medical image in the common region; and determining whether the first medical image and the second medical image are medical images of the same patient based on the correlation coefficient.