an embedding processing section which embeds sub-information in main image information in an invisible state by performing color difference modulation, thereby creating composite image information;

an image processing section which doubles the number of pixels of the composite image information created by the embedding processing section in a sub-scanning direction of a recording device, and performing thinning-out processing in correspondence with pixel formation processing in the image recording apparatus; and

a recording section which records the composite image information processed by the image processing section on a recording medium by using an alternate driving/recording scheme of alternately forming odd-numbered and even-numbered pixels in a main scanning direction of the recording device on a recording line basis and conveying the recording medium with a convey pitch ½ a pixel pitch in the main scanning direction.