1. An image generating device comprising: a human detector that detects a human from a captured image; a motion detector that detects a motion between frames from the captured image, each of the frames being a unit of an image; an attitude detector that detects an attitude of an imaging device by a panning or a tilting operation of the imaging device; a cut-out frame deciding unit that decides a cut-out frame for cutting out a part from the captured image based on a constraint condition on the detected human and the detected motion, and a constraint condition regarding camerawork between the frames based on the detected attitude; and a composition information shaping unit that generates an image different from the captured image using attribute information of the captured image including the cut-out frame.