An original document is formed using a first print medium by printing a first and second monochrome patterns with a single colorant to form printed first and second regions including first and second shapes, respectively, which are devoid of the colorant. The second shapes have a smaller size and a higher frequency than the first shapes. The first and/or second regions encode information. The first and second patterns and a fluorescence of the first print medium are selected such that the first and second regions of the original document are indistinguishable to the naked eye, under both normal and ultraviolet illumination but are distinguishable, only under the ultraviolet illumination, in a copy formed by scanning the original document and printing the scanned document on a second print medium with a plurality of colorants, to reveal the encoded information.

An image formation system includes: an encoded image generation device including a first processor that generates print data from manuscript data, sets security information for controlling a print mode of the print data, and generates an encoded image from the print data and the security information; and an image formation device including a second processor that inputs the encoded image, decodes the print data and the security data from the input encoded image, determines whether an output of the decoded print data is available in accordance with the decoded security information, and outputs the decoded print data when it is determined that the output of the print data is available.

An image reading device includes a marking part that applies a predetermined mark to a margin of a rear end of a document having passed through an image reading position, a mark erasing part that erases the predetermined mark when the document is discharged from a sheet discharge port, and an image data processing unit that determines whether the predetermined mark exists in image data of a document image read by an image reading unit and erases the image data of the document image when it is determined that the predetermined mark exists.

An image forming apparatus including an image forming unit, a unit holder, and circuitry is provided. The image forming unit includes a color toner unit, a replaceable black toner unit, and a replaceable special toner unit that form a color toner image, a black toner image, and a special toner image, respectively. The unit holder selectively and detachably holds the replaceable black toner unit or the replaceable special toner unit. The circuitry controls the image forming unit to perform: a normal operation, when the unit holder holds the replaceable black toner unit, that forms a color-black image; a special operation, when the unit holder holds the replaceable special toner unit, that forms a color-special image; and a toner amount increase control that increases an amount of the color toner per unit area in the color toner image in the special operation than that in the normal operation.

An image forming apparatus including an image forming unit, a fixing device, and circuitry is provided. The image forming unit is configured to perform a special image forming operation that forms a color toner image and a special toner image with a color toner and a special toner, respectively, on a recording medium and a normal image forming operation that forms the color toner image without forming the special toner image on the recording medium. The fixing device is configured to fix the color toner image and the special toner image on the recording medium. The circuitry is configured to perform, in the special image forming operation, a toner amount suppression control that makes an amount of the color toner on the recording medium per unit area smaller than that in the normal image forming operation.

An image formation system includes: an encoded image generation device including a first processor that generates print data from manuscript data, sets security information for controlling a print mode of the print data, and generates an encoded image from the print data and the security information; and an image formation device including a second processor that inputs the encoded image, decodes the print data and the security data from the input encoded image, determines whether an output of the decoded print data is available in accordance with the decoded security information, and outputs the decoded print data when it is determined that the output of the print data is available.