A public key encryption system for authenticating an image includes a digital camera having embedded therein a private key unique to the digital camera. A known public key uniquely based upon the private key is used to decrypt digital data encrypted with the private key to establish authenticity of the image. The encryption system further comprises means for generating one or more patterns each composed of at least one individual area that is visible together with the image of the object, means for designating at least one individual area as an active area of the image suitable for authentication and for generating location data identifying the active area, and means for calculating image hash from image data of the active area of the image using a predetermined hash algorithm. The image hash is then encrypted with the embedded private key, thereby producing a digital signature uniquely associated with the active area of the image, and the image data, the digital signature, and the location data of said active area are stored in a digital record. By confining encryption to this selected region of interest, power requirements for subsequent hashing and encryption are reduced, which is an advantage for portable devices such as a digital camera.