An image processing apparatus separates input image data into low resolution image data and one or more auxiliary image data for interpolating the low resolution image data, and decrypts at least one of the separated auxiliary image data. The image processing apparatus also separates input image data into low resolution image data and at least one auxiliary image data for interpolating the low resolution image data and decodes the image data with at least one of the auxiliary image data being encrypted, and decrypts the encrypted auxiliary image data and synthesizes the low resolution image data with the auxiliary image data.