1. An image processing apparatus comprising: a display screen displaying a first image included in a continuously taken image group; a friction position detector detecting a friction position on the display screen rubbed by a user; and an image synthesizing unit synthesizing a pixel area of the first image corresponding to the friction position, and a pixel area of a second image included in the image group; wherein the image synthesizing unit switches the second image to be synthesized with the first image so as to increase an imaging time difference between the first image and the second image along with an increase in the amount of friction rubbed by the user.