1. A subject information acquiring device comprising: an acoustic detector configured to convert an acoustic wave propagated in a subject into an electrical signal; and a data processing unit configured to acquire a subject information distribution as pixel or voxel data using the electrical signal, wherein said data processing unit holds a plurality of items of template data, each item indicating a relationship between a real image and an artifact which is a virtual image accompanying the real image, the plurality of items being different from each other, wherein said data processing unit is configured to calculate a plurality of similarities respectively between the plurality of items of template data and the subject information distribution, wherein said data processing unit is configured to acquire an integrated similarity distribution using the plurality of similarities, and wherein the plurality of items of template data correspond respectively to optical absorbers of different sizes.