A density signal value determination method, an image forming apparatus, and an image processing system are configured to automatically and optimally determine the density of a copy-forgery-inhibited pattern image that includes a latent image and a background image. In a density signal value determination method, a test sheet, on which a plurality of latent image patches and a plurality of background image patches are formed, is outputted. Subsequently, the luminance, the density, and the reflection density of each of the patches are obtained from image data obtained by reading this test sheet. Then, an optimal combination of a latent image patch and a background image patch is selected according to the obtained values. Finally, density signal values used to generate the selected patches are set to generate a latent image and a background image.