1. An image processing apparatus which processes time-series images picked up by an imaging device in time series, comprising: a motion-vector calculating unit that calculates a motion vector between plural images constituting the time-series images with respect to plural pixel regions set in the image; a newly-appearing-rate estimating unit that estimates a newly-appearing rate, which is a rate of a newly-appeared region in an image between the plural images, based on a motion vector calculated by the motion-vector calculating unit; and a display-time calculating unit that calculates a display time of the image according to a newly-appearing rate estimated by the newly-appearing-rate estimating unit.