1. An image processing apparatus comprising: a specific sound detecting section which detects a specific sound generated during motion of a specific motion conducted by a target object included in an image group including a plurality of images which continues in a time-series manner; a synthetic image generating section which generates a synthetic image representing transitions of the specific motion using a predetermined number of images included in a selection range of the image group in a time axis, with reference to a detection position of the detected specific sound in the time axis; a determination range setting section which sets, as a determination range, a range in the time axis for determination on the generation of the synthetic image on the basis of a user manipulation; an object distance calculating section which calculates a distance to the target object; a delay time calculating section which calculates a delay time of the detected specific sound on the basis of the calculated distance; and a control section which corrects the detection position of the detected specific sound in the time axis on the basis of the calculated delay time and determines whether or not to allow the synthetic image generating section to generate the synthetic image according to whether the corrected detection position exists in the set determination range.