The provided is an image processing technology to avoid inaccuracy of inferring a position of an object due to wrong model assumption.An image processing device according to an exemplary aspect of the present invention includes: a matching unit 106 that estimates similarity of input image to particle images including areas of particles at relative positions, true positions of the particles in the particle images being given; and a calculation unit 108 that calculates positions of particles in the input image based on the similarity and the true positions.