The image data with the copy-forgery-inhibited pattern image added and an image area flag signal stored in the hard disk drive are inputted into a thinning filter. A thinning circuit does not perform thinning processing on these pieces of data and outputs the inputted image, as it is. The filter performs processing so that an image of a copy-forgery-inhibited pattern background part may be deleted. A selector selects an image signal not passing through the filter for a latent mark of the copy-forgery-inhibited pattern whose image area flag is set as "Character," and select an image signal subjected to the processing by the filter for a copy-forgery-inhibited pattern background part whose image area flag is set as "Photograph." By doing so, it is possible to perform low pass processing on only the copy-forgery-inhibited pattern background part and perform processing of making a latent-mark part emerge.