A photoacoustic image evaluation apparatus comprising: a photoacoustic image acquisition unit configured to acquire a first photoacoustic image generated at a first point in time and a second photoacoustic image generated at a second point in time before the first point in time, the first and second photoacoustic images being photoacoustic images generated by detecting photoacoustic waves generated inside a subject, who has been subjected to blood vessel regeneration treatment, by emission of light into the subject, the first photoacoustic image being a current photoacoustic image, the second photoacoustic image being a past photoacoustic image stored in a past image storage unit; a registration processing unit configured to perform (i) low pass filter processing on the first photoacoustic image and the second photoacoustic image, whereby a cutoff frequency of the low pass filter is set so as to extract image components of blood vessels having thicknesses of 300 μm or more, and, after the low pass filter processing, (ii) registration processing between the first photoacoustic image and the second photoacoustic image, such that registration processing between blood vessels having a thickness of 300 μm or more, among blood vessels included in the first photoacoustic image and the second photoacoustic image, is performed; a blood vessel region extraction unit configured to extract a first blood vessel region included in the first photoacoustic image and a second blood vessel region included in the second photoacoustic image, a blood vessel regeneration index acquisition unit configured to acquire a blood vessel regeneration index, which indicates a state of a blood vessel by the regeneration treatment, based on a difference between a blood vessel included in the first photoacoustic image and a blood vessel included in the second photoacoustic image; and a display control unit configured to display the blood vessel regeneration index on a display unit; wherein the blood vessel regeneration index acquisition unit acquires the blood vessel regeneration index based on a difference between the first blood vessel region and the second blood vessel region registered by the registration processing. a photoacoustic image acquisition unit configured to acquire a first photoacoustic image generated at a first point in time and a second photoacoustic image generated at a second point in time before the first point in time, the first and second photoacoustic images being photoacoustic images generated by detecting photoacoustic waves generated inside a subject, who has been subjected to blood vessel regeneration treatment, by emission of light into the subject, the first photoacoustic image being a current photoacoustic image, the second photoacoustic image being a past photoacoustic image stored in a past image storage unit; a registration processing unit configured to perform (i) low pass filter processing on the first photoacoustic image and the second photoacoustic image, whereby a cutoff frequency of the low pass filter is set so as to extract image components of blood vessels having thicknesses of 300 μm or more, and, after the low pass filter processing, (ii) registration processing between the first photoacoustic image and the second photoacoustic image, such that registration processing between blood vessels having a thickness of 300 μm or more, among blood vessels included in the first photoacoustic image and the second photoacoustic image, is performed; a blood vessel region extraction unit configured to extract a first blood vessel region included in the first photoacoustic image and a second blood vessel region included in the second photoacoustic image, a blood vessel regeneration index acquisition unit configured to acquire a blood vessel regeneration index, which indicates a state of a blood vessel by the regeneration treatment, based on a difference between a blood vessel included in the first photoacoustic image and a blood vessel included in the second photoacoustic image; and a display control unit configured to display the blood vessel regeneration index on a display unit; wherein the blood vessel regeneration index acquisition unit acquires the blood vessel regeneration index based on a difference between the first blood vessel region and the second blood vessel region registered by the registration processing.