1. An image forming apparatus for generating a copy-forgery-inhibited pattern image which includes a latent image area drawn using a large dot pattern and a background area drawn using a small dot pattern, the latent image being encoded and embedded in the copy-forgery-inhibited pattern image as additional information, comprising: a large dot pattern decision unit, configured to read a large dot test pattern image printed using a plurality of large dot test patterns, recognize encoded additional information embedded in each large dot test pattern by decoding the additional information, obtain a recognition rate of the additional information and an average density of each large dot test pattern, and select, as a large dot pattern for use in recording, a large dot pattern corresponding to a large dot test pattern whose recognition rate falls with a predetermined recognition rate range and is close to a predetermined recognition rate reference value and whose average density falls within a predetermined density range and is close to a predetermined density reference value; a small dot pattern decision unit, configured to read a small dot test pattern image printed using a plurality of small dot test patterns, obtain an average density of each small dot test pattern, and select, as a small dot pattern for use in recording, a small dot pattern corresponding to a small dot test pattern whose average density falls within the predetermined density range and is close to the average density of the large dot pattern selected for use in recording; and a print image generator, configured to generate a copy-forgery-inhibited pattern image by drawing a foreground using the large dot pattern selected for use in recording by said large dot pattern decision unit, the foreground containing predetermined encoded additional information, and drawing a background using the small dot pattern selected for use in recording by said small dot pattern decision unit, and to combine the copy-forgery-inhibited pattern image with a print target image.