An image processing device includes a frequency calculation part configured to calculate frequency coefficients of an image, a coefficient selection part configured to select plural pairs of the frequency coefficients from the calculated frequency coefficients, a code generation part configured to generate a code based on a comparison result between an absolute value of a difference between the two frequency coefficients of each of the selected pairs and a threshold, and a magnitude relationship between the two frequency coefficients, and a signature generation part configured to encrypt the generated code with a private key to generate a digital signature.