Provided are an image processing device, etc. that, even when two or more types of tissue are present in a subject, can accurately estimate the depth at which a specific tissue is present. An image processing device 100 that, on the basis of an image captured of a subject using light of a plurality of wavelengths, estimates the depth of a specific tissue contained in the subject, the image processing device being provided with: an absorbance calculating unit 141 that, on the basis of the pixel value of each of a plurality of pixels that constitute the image, calculates absorbance at the plurality of wavelengths； a component-quantity estimating unit 142 that, on the basis of the absorbance, uses a plurality of reference spectra for different tissue depths to estimate each of a plurality of component quantities for each of two or more absorption components that are included in each of two or more tissues that contain the specific tissue； a proportion calculating unit 143 that calculates proportions at least for the plurality of component quantities that have been estimated for absorption components included in the specific tissue； and a depth estimating unit 144 that, on the basis of the proportions, estimates the depth, within the subject, of at least the specific tissue.La présente invention concerne un dispositif de traitement d'image, etc. qui, même lorsque deux ou plusieurs types de tissu sont présents dans un sujet, permet d'estimer avec précision la profondeur à laquelle un tissu spécifique est présent. L'invention porte en particulier sur un dispositif de traitement d'image (100) qui, sur la base d'une image capturée d'un sujet au moyen de la lumière d'une pluralité de longueurs d'onde, estime la profondeur d'un tissu spécifique contenue dans le sujet, le dispositif de traitement d'image étant pourvu des éléments suivants : une unité de calcul d'absorbance (141) qui, sur la base de la valeur de pixel de chacun d'une pluralité de pixels qui constituent l'image,
