Patent ID: 8134752

Claim:
An image forming apparatus, comprising: an image forming section for forming an image on a sheet; a data receiving section for receiving image data for use in forming a background pattern as inputted to the image forming apparatus; a background pattern forming section for forming a background pattern which includes a background portion formed with a first screen ruling and a latent image portion formed with a second screen ruling which is higher than the first screen ruling in accordance with the image data for use in forming the background pattern as received by the data receiving section, with a copy prohibiting pattern embedded in the background portion; a determining section for determining if an area of the background portion occupied in the background pattern formed by the background pattern forming section is smaller than a predetermined threshold value; and a background pattern correcting section which corrects, when the determining section determines that the area of the background portion is smaller than the threshold value, the background portion and the latent image portion so that the area of the background portion becomes equal to or larger than the threshold value by reducing the latent image portion while maintaining the second screen ruling, and which forms a background pattern having a corrected background portion in which a copy prohibiting pattern is embedded, wherein the image forming section forms on a sheet the background pattern as formed by the background pattern correcting section when the determining section determines that the area of the background portion is smaller than the threshold value, and forms on the sheet the background pattern as formed by the background pattern forming section when the determining section determines that the area of the background portion is equal to or larger than the threshold value.