1. An image processing apparatus comprising: a computer including processing circuitry configured to at least: generate a first perspective image of a target viewed in a first direction, based on three-dimensional volume data of the target; acquire a second perspective image of the target viewed in a second direction; acquire initial positions of one or more pairs of first and second corresponding points respectively on the first and second perspective images; update the first direction and the position of the first corresponding point, based on the difference in position of the target between the first and second perspective images; regenerate the first perspective image viewed in the updated first direction; and generate a first display image including the regenerated first perspective image and the second perspective image, the updated first corresponding point on the regenerated first perspective image, and the second corresponding point on the second perspective image.