An image processing apparatus and a control method thereof. Information of image processing parameters, such as halftoning, edge emphasis, color correction, and gamma correction, is inserted into the document to be printed in the form of the watermark during the printing work. Thus, when the user wants to copy the printed document, the information of the image processing parameters used for printing the document is optimized suitable for the copy by detecting the watermark inserted into the printed document, thereby improving the quality of the copy. The method includes inserting first information of image processing parameters, which are used to print the document, into the document when printing the document, and optimizing second information of image processing parameters to be used for copying the document using the first information of image processing parameters inserted into the document when copying the document.