1. An image processing apparatus generating animation data to generate a face image of a different expression on the basis of a face image, the image processing apparatus comprising: first eyes-and-mouth detecting means for detecting eye boundaries between eyeballs and eyelids where eyeballs are exposed and a mouth boundary between lips and the inside of a mouth from a first face image, which is a face image of a first expression; second eyes-and-mouth detecting means for detecting eye boundaries and a mouth boundary from a second face image, which is a face image of a second expression different from the first expression; first skin model generating means for generating a first skin model, which is a face model generated by removing only the inside of the eye boundaries and the inside of the mouth boundary from the first face image; second skin model generating means for generating a second skin model, which is a face model generated by removing only the inside of the eye boundaries and the inside of the mouth boundary from the second face image; inside-of-mouth model generating means for generating an inside-of-mouth model, which is a model of the inside of the mouth boundary; eyeball model generating means for generating an eyeball model, which is a model of eyeballs; first deformation parameter generating means for generating a first deformation parameter used to deform the first skin model to the second skin model; second deformation parameter generating means for generating a second deformation parameter used to deform the second skin model to the first skin model; and output means for outputting the first and second skin models, the first and second deformation parameters, the inside-of-mouth model, and the eyeball model as the animation data.