An image processing apparatus includes an input section, a specification section, an extraction section, and a calculation section. The input section receives fluorescence image information obtained by picking up an image of fluorescence based on application of excitation light to a subject provided with a fluorescent substance with a specific effect on a living tissue and therapeutic light position image information including an application position of therapeutic light. The specification section specifies an application region of the therapeutic light. The extraction section extracts a luminance value corresponding to the application region of the therapeutic light and a luminance value corresponding to a region other than the application region of the therapeutic light. The calculation section calculates and outputs a ratio of the extracted luminance value corresponding to the application region to the luminance value corresponding to the region other than the application region.
