1. An image processing apparatus for identifying an object in an input image, comprising: a calculation unit configured to obtain a degree of similarity between corresponding local feature amounts out of a plurality of local feature amounts of the object in the input image and a plurality of local feature amounts of an object in an image registered in advance; a derivation unit configured to select at least one degree of similarity out of the degrees of similarity obtained by said calculation unit based on a capturing condition for the object in the input image and a capturing condition for the object in the registered image and derive one degree of similarity from the at least one selected degree of similarity; and a determination unit configured to determine based on the one degree of similarity derived by said derivation unit whether the object in the input image belongs to the same category as the object in the registered image.