1. A non-transitory computer readable storage medium storing a program that causes a computer to execute a process comprising: obtaining a first image of a chest and a second image of the chest scanned after the first image; specifying a plurality of difference vectors indicating a changes of a plurality of positions in a lung between the first image and the second image; determining whether a change in the lung occurs, the change being a change indicated by specified difference vectors, in the plurality of difference vectors, toward a specified position in the lung; transforming the second image to adjust the plurality of positions in the second image to the plurality of positions in the first image based on the plurality of difference vectors far from the specified position by a predetermined distance or more; and outputting the transformed second image on a display device.