A digital evidential camera system is for detecting the alteration of image data obtained by photographing an object. The system comprises the camera and an alteration detection unit. The camera includes an image pickup unit for picking up an image of the object and an encryption processing unit for generating the alteration detection data using an encryption key built therein from the image data obtained by the image pickup unit. The alteration detection unit decrypts the alteration detection data using a decryption key corresponding to the encryption key, and detects whether the image data is altered based on the result of decryption.