To achieve an objective of implementing authentication with high precision, even when image-capturing conditions differ among registered images, an image authentication apparatus (1) of the present invention has registered images (R) obtained by capturing images of people, and image-capturing conditions pertaining to the faces of the people in the registered images (R) registered in association with each other in a registered image database (21), and is provided with: a face-information data estimation unit (33) for estimating face-information data of an inputted image (A1); a weighting determination unit (34) for determining weighting in accordance with the similarities between face-information data of registered images (R) and the face-information data of the inputted image (A1); an authentication score calculation unit (35) for calculating authentication scores between the inputted image (A1) and the registered images (R); a weighted authentication-score calculation unit (36) for applying, to the authentication scores, weighting determined for the corresponding registered images (R); and an authentication result output unit (37) for verifying the inputted image (A1) on the basis of the weighted authentication scores.