1. An image measurement device comprising: an illumination unit including a plurality of light sources that irradiate light beams having different peak wavelengths; a staining method obtaining unit configured to obtain information indicating a staining method of an inspection pathology specimen; an image obtaining unit configured to: select a combination of light sources included in the plurality of light sources in the illumination unit according to the staining method indicated by the information obtained by the staining method obtaining unit, based on illumination information in which each of one or more staining methods including the staining method is associated with a corresponding one of one or more combinations of light sources including the combination of light sources; and capture inspection images of the inspection pathology specimen with light beams sequentially irradiated from the respective light sources in the selected combination, and capture reference images of a reference pathology specimen with light beams sequentially irradiated from the respective light sources included in the plurality of light sources; a calculating unit configured to calculate a positivity that is a percentage of positive cell nuclei in the inspection pathology specimen, based on the inspection images obtained by the image obtaining unit; an ortho-normalization unit configured to form a plurality of spectral distribution vectors from the reference images, and calculate an ortho-normalization base vector from the plurality of spectral distribution vectors; and an evaluation unit configured to associate the staining method of the reference pathology specimen with the combination of light sources to generate the illumination information, and store the illumination information in a recording medium, the combination of light sources having an evaluation value that exceeds a reference value or is largest among evaluation values of combinations of light sources in the illumination unit, each evaluation value being a total value of coefficients of ortho-normalization base vectors included in a linear sum of the ortho-normalization base vectors when a spectral distribution of the illumination unit is represented as the linear sum.