1. An image processing apparatus comprising: a pre-combination processing unit configured to perform a pre-combination process so that a plurality of frames of image data having continuity in time are used as combination-use image data to be combined; an operation detection unit configured to detect operation input information used for a combination process; and a combination processing unit configured to perform a combination process on the combination-use image data of the plurality of frames obtained in the pre-combination process according to the operation input information detected by the operation detection unit so as to generate combined-image data representing a still image, wherein the combination processing unit determines a flash image that has been captured using a flash among the combination-use image data having continuity in time, and performs a combination process on the combination-use image data by changing a weighting coefficient of at least the flash image to generate combined-image data in which a flash effect has been removed.