1. An image-processing apparatus comprising: taken-image acquisition means for acquiring a taken image; to-be-processed area setting means for carrying out an analysis on the taken image and for using a pixel area of a photographed-subject image of a specific type in said taken image as a to-be-processed area of an image conversion process in accordance with a size of said photographed-subject image if a result of said analysis indicates that said photographed-subject image exists in said taken image; and conversion means for carrying out said image conversion process on said photographed-subject image with said pixel area thereof used as said to-be-processed area in order to generate a post-conversion image obtained as a result of said image conversion process, wherein: said to-be-processed area setting means produces a first result of determination as to whether said taken image is taken in a manual photographing with a timing set by a manual operation or taken in an automatic photographing carried out automatically; if the first result of said determination indicates that said taken image is taken in the manual photographing with the timing set by the manual operation, said to-be-processed area setting means produces a second result of determination as to whether the size of the photographed-subject image of the specific type in said taken image is small or large and, if the second result of said determination indicates that said size of said photographed-subject image of the specific type is small, said to-be-processed area setting means uses the pixel area of said photographed-subject image of the specific type in said taken image as the to-be-processed area of the image conversion process; and if the first result of said determination indicates that said taken image is taken in the automatic photographing, said to-be-processed area setting means produces a third result of determination as to whether the size of the photographed-subject image of the specific type in said taken image is small or large and, if the third result of said determination indicates that said size of said photographed-subject image of the specific type is large, said to-be-processed area setting means uses the pixel area of said photographed-subject image of the specific type in said taken image as the to-be-processed area of the image conversion process.