1. A composite image generating apparatus comprising: a first storage unit configured to store a motion to be combined and first part image data such that the motion and the first part image data correspond to each other; an input unit configured to input a plurality of items of image data; a first determining unit configured to determine whether or not a movement of a part changing over a plurality of items of the image data input by the input unit is substantially the same as the motion stored in the first storage unit; a first composite unit configured to read the first part image data stored in the first storage unit correspondingly to the motion and combine the first part image data with the image data having the changing part, if the first determining unit determines that the movement is substantially the same as the motion; a second storage unit configured to store a plurality of target image data to be replaced; a second determining unit configured to determine whether or not the image data input by the input unit includes the target image data stored in the second storage unit; and a second composite unit configured to add specific image data to the combined image data produced by the first composite unit based on a positional relationship between the target image data and the image data having the changing part to produce composite image data, if the second determining unit determines that the input image data includes the target image data.