An additional data useful for the management of copies of a document for an image forming apparatus is embedded in a hard copy of the document. The additional data is embedded in an inherent image of a document as discrete dots arranged in a prescribed format. Preferably, the size of each of said discrete dots is not so large as to be recognized easily with naked eyes. The additional data can be embedded in unit of blocks. Further, the density of the discrete dots is different from the density adjacent to the discrete dots. The image data for embedding an additional data can be obtained by reading a document, or by receiving data sent from a computer or read from a floppy disk. An additional data embedded in a hard copy can be extracted from the image data on the hard copy. Further, the production of a copy according to the image data can be controlled according to the extracted additional data. For example, if the additional data means that the source of the hard copy is a secret document, the copying is allowed only for a legitimate user. An additional data is generated for each copy according to the extracted additional data for embedding it in a hard copy to identify each copy. The additional data generated for each copy are compiled and they are used to manage copies of various sources systematically and illegal copies can be traced easily. If the additional data received from a printer is not consistent with the additional data already stored, the printing may be prohibited. A transmitter for transmitting an additional data may be provided in a document such as a book.