1. An image processing apparatus comprising: a detection unit configured to detect a region of a face of a person from an input image; an extraction unit configured to extract an image feature amount from the region of the face; a projection unit configured to generate a plurality of projected feature vectors by projecting a feature vector indicating the image feature amount onto each of a plurality of feature spaces corresponding to plural ranges of directions of a face; a classification unit configured to classify a direction of the face into one of the plural ranges of directions based on the plurality of projected feature vectors; a vector selection unit configured to select one of the plurality of projected feature vectors corresponding to the classified range of directions of the face; and an estimation unit configured to estimate, based on the selected one of the projected feature vectors and a model corresponding to the classified range of directions of the face, a detailed direction of the face belonging to the classified range of directions.