1. A method for processing an image on a portable terminal equipped with a dual camera, the method comprising: selecting an image synthesis mode; performing a simultaneous or a sequential photographing of a front camera and a rear camera; obtaining a first image and a second image through the front camera and the rear camera; detecting an object image from one of the first image and the second image; and generating a synthesized image by synthesizing the object image to the other of the first image and the second image in which the object image was not detected.