An image sensing apparatus includes an image sensing unit and a key data control unit. The image sensing unit generates image data of a sensed image. The key data control unit (a) generates key data if a user turns on the power of the image sensing apparatus, and (b) erases the key data from the image sensing apparatus if a user turns off the power of the image sensing apparatus. The key data is used to generate authentication data. The authentication data is used to authenticate whether the image data is altered.