An identification device configured to perform an authenticity determination of a product on which a counterfeit prevention medium is attached, the device comprising: a reference image generation unit configured to generate a reference image data corresponding to an observation angle, for comparing the reference image data with captured image data where the counterfeit prevention medium is captured, with a pattern of light to be observed of the counterfeit prevention medium changing depending on the observation angle, the observation angle being an angle formed between a reference line of a surface to be observed of the counterfeit prevention medium and an imaging direction of the captured image data; an observation angle estimating unit configured to calculate, from the captured image data, a position and an imaging direction at/in which the captured image data has been captured in a three-dimensional space where the counterfeit prevention medium is placed when the captured image data has been captured, on the basis of a predetermined coordinate conversion equation, and calculate the observation angle on the basis of the position and the imaging direction; an available image selection unit configured to determine whether the observation angle of the captured image data is within a determinable range enabling authenticity determination based on an optical change of the counterfeit prevention medium, select available captured image data available for the authenticity determination from the captured image data, and output the available captured image data as an available image data; and a similarity calculating unit configured to calculate a similarity between the available image data and the reference image data; an authenticity determination unit configured to perform an authenticity determination whether the counterfeit prevention medium is correct, on the basis of whether the similarity exceeds a predetermined threshold; wherein the captured image data is captured using a general purpose digital camera or a mobile terminal. a reference image generation unit configured to generate a reference image data corresponding to an observation angle, for comparing the reference image data with captured image data where the counterfeit prevention medium is captured, with a pattern of light to be observed of the counterfeit prevention medium changing depending on the observation angle, the observation angle being an angle formed between a reference line of a surface to be observed of the counterfeit prevention medium and an imaging direction of the captured image data; an observation angle estimating unit configured to calculate, from the captured image data, a position and an imaging direction at/in which the captured image data has been captured in a three-dimensional space where the counterfeit prevention medium is placed when the captured image data has been captured, on the basis of a predetermined coordinate conversion equation, and calculate the observation angle on the basis of the position and the imaging direction; an available image selection unit configured to determine whether the observation angle of the captured image data is within a determinable range enabling authenticity determination based on an optical change of the counterfeit prevention medium, select available captured image data available for the authenticity determination from the captured image data, and output the available captured image data as an available image data; and a similarity calculating unit configured to calculate a similarity between the available image data and the reference image data; an authenticity determination unit configured to perform an authenticity determination whether the counterfeit prevention medium is correct, on the basis of whether the similarity exceeds a predetermined threshold; wherein the captured image data is captured using a general purpose digital camera or a mobile terminal.