An image forming apparatus includes an image inputting section through which image information containing object information and secure object information is received, the object information representing at least one object and the secure object information indicating an object that should be protected against tampering. A first image-data generator generates first image data for forming an image, the first image data being generated in accordance with the object information. A secure object identifying section identifies a secure object based on the secure object information. A characteristic information detector extracts at least a part of the object information on the secure object, the part of the object information being a characteristic information on the secure object. A second image-data generator generates second image data for forming a characteristic image representing the characteristic information. An image data combiner combines the first image data and the second image data. An image forming section forms an image in accordance with the image data combined in the image data combiner.