1. An image processing apparatus comprising: an image acquisition unit that acquires image information representing a fluorescence observation image of a specimen stained with hematoxylin-eosin; a spectrum generation unit that generates a plurality of spectra each representing a wavelength distribution of fluorescence intensity in a plurality of pixels in the fluorescence observation image; a pixel extraction unit that extracts at least two pixel groups with a feature of a particular spectrum from the plurality of pixels, wherein the pixel extraction unit is configured to: extract the at least two pixel groups with reference to at least two fluorescence intensity spectra acquired respectively in advance with respect to at least two kinds of components in the specimen; extract pixel groups having the same peak wavelengths as those of the at least two fluorescence intensity spectra, as the at least two pixel groups, respectively; extract a pixel group having a peak wavelength of 560 nm as a pixel group representing an elastic fiber in the specimen; and extract a pixel group having a peak wavelength of 570 nm as a pixel group representing a blood corpuscle in the specimen; an image generation unit that generates an image based on the extracted pixel groups; and an abnormality determination unit that determines a presence or absence of abnormality in a blood vessel in the fluorescence observation image based on the pixel group representing the elastic fiber.