1. An image processing apparatus comprising: a generating section for generating watermark data associated with a chromatic or achromatic watermark for copy control, which appears as a result of making a copy; a composing section for generating composite image data associated with an image composed by joining an original image with a watermark for copy control, on a basis of the watermark data generated by the generating section and original image data obtained by reading an original document; and a determinating section for determining whether the original document includes a chromatic color or not, on a basis of the original image data, wherein the composing section generates composite image data on a basis of generated watermark data and the original image data when the determinating section determines that the original document includes a chromatic color, wherein the composing section generates composite image data on a basis of generated achromatic watermark data and the original image data when the determinating section determines that the original document does not include a chromatic color, wherein the generating section generates watermark data associated with an achromatic color and watermark data associated with a chromatic color, the image processing apparatus further comprising: a storage section for storing the watermark data generated by the generating section; and a selection section for selecting one from the watermark data associated with an achromatic color and the watermark data associated with a chromatic color stored in the storage section, on a basis of a determination result by the determinating section; wherein the composing section joins the original image data with the watermark data selected by the selection section.