1. An image processing apparatus comprising: an extraction unit that extracts corresponding partial features from an input pattern and a registration pattern as a preregistered pattern; a composition unit that generates a plurality of combinations of the partial features as composited partial features; a measurement unit that measures a quantity of the partial features which belong to the composited partial feature, correspond to each other in the input pattern and the registration pattern, and satisfy a predetermined criterion; an evaluation unit that evaluates the partial features based on the measurement result from said measurement unit; and an identification unit that identifies, among classes to which respective registration patterns belong, a class corresponding to the input pattern based on the evaluation result from said evaluation unit.