1. An image processing apparatus comprising: a processor; and a memory storing instructions that, when executed by the processor, cause the image processing apparatus to perform: acquiring target image data indicating a target image, which is a target of an image processing, and template image data indicating a template image; detecting a face area indicating a face in the target image; specifying a partial image in the target image based on a detection result of the face area; and generating composited image data indicating a composited image by compositing the specified partial image in a specific area in the template image, wherein, when a single face area is detected in the target image, a first partial image, which includes the single face area and has a size determined based on a size of the single face area, is specified as the partial image in the target image, and wherein, when a plurality of face areas are detected in the target image, a second partial image, which includes at least one of the plurality of face areas, has a shape homothetic to the specific area, and has a maximum size which may be taken from the target image as being homothetic to the specific area, is specified as the partial image in the target image.