1. An image processing apparatus, characterized by comprising: an image obtaining unit which obtains an image in which a first biological pattern and a second biological pattern having different textures are superimposed; a normalizing unit which normalizes density of said image on the basis of an average and a standard deviation of pixel values inside a local region in said image using the size of said local region and at least one other parameter in accordance with difference in texture between said first biological pattern and said second biological pattern to thereby separate said first biological pattern and said second biological pattern in said image; and a pattern collating unit which collates a known pattern for collation with each of said first biological pattern and said second biological pattern separated by said normalizing unit wherein said first biological pattern is a blood vessel pattern and said second biological pattern is a fingerprint.