1. An image processing apparatus comprising: an information acquiring portion that acquires setting information of a printer driver on image process conditions for processing image data, the setting information including information on an angle of a screen lattice used for pseudo-tone processing; a creating portion that creates additional image data, serving as a watermark image, to be embedded into the image data based on the acquired information on the image process conditions and additional information; and a merging portion that merges the image data with the additional image data to create composite image data, wherein the creating portion creates a pattern image of an integral multiple of a screen shape, which is converted from a rectangular shape to a parallelogram shape by an affine process; wherein the pattern image has a size adjusted according to a print resolution and wherein the merging portion selects pattern images corresponding to the additional information and arranges multiple pattern images in a given order.