In an image input apparatus provided with an image pick-up unit, an image signal generated by the image pick-up unit is converted into digital information. The digital information is then encrypted by using an encryption key. The encryption key is input into the image input apparatus from an external apparatus, such as an IC card. The image input apparatus erases the encryption key after the digital information has been encrypted. With this arrangement, unauthorized users can be prevented from obtaining the encryption key, and different encryption keys can be assigned to a plurality of users. Thus, the privacy and the security of the image information can be enhanced, and the copyright of the image information can be protected more reliably.