1. An image processing apparatus, comprising: a processor programmed to execute a method including: obtaining a standard observation image obtained by imaging blood vessels irradiated with white light and a fluorescent image by imaging fluorescence emitted by substances within the blood vessels when an excitation light beam is irradiated onto the blood vessels; generating a plurality of spectral images, each of a different wavelength range, of the same blood vessels of which the fluorescent image is obtained, by administering matrix calculations onto the standard observation image according to matrix parameters that are extracted from a database as corresponding to respective wavelengths of the spectral images to be generated; judging whether blood vessel images are present in each of the plurality of spectral images and judging the depth position at which the blood vessels exist based on a wavelength corresponding to the spectral image in which the blood vessel images are judged to be present; and changing image processing conditions according to the judged depth position of the blood vessels, and administering a blood vessel emphasizing process on the fluorescent image.