Patent Publication Number: US-2012038941-A1

Title: Image forming apparatus, information processing apparatus, image forming system, and image forming method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from: U.S. provisional application 61/372,441, filed on Aug. 10, 2010; the entire contents all of which are incorporated herein by reference. 
    
    
     FILED 
     Embodiments described herein relate generally to a technique for preventing leakage of information. 
     BACKGROUND 
     In the past, an image forming apparatus including a unit configured to perform printing with an unerasable toner and a unit configured to perform printing with an erasable toner is developed. 
     Even after the erasable toner is erased, in some cases, the erased toner develops a color again according to a temperature change or the like. If a confidential document is erased after being printed with an erasable toner and flows out to outside the company, the confidential document develops a color again, changes to a visible state, and flows out to outside the company. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of the configuration of an image forming system according to a first embodiment; 
         FIG. 2  is a block diagram of an image forming apparatus according to the first embodiment; 
         FIG. 3  is a flowchart for explaining an operation example of the image forming apparatus according to the first embodiment; 
         FIG. 4A  is a diagram of an example of a watermark; 
         FIG. 4B  is a diagram for explaining woven pattern printing; 
         FIG. 5  is a flowchart for explaining an operation example of the image forming apparatus according to the first embodiment in the case of acquisition of a page description language; 
         FIG. 6A  is a diagram of an example of the page description language; 
         FIG. 6B  is a diagram of an example of a raster image; 
         FIG. 7  is a diagram for explaining a problem in the past; 
         FIGS. 8A and 8B  are diagrams of operation examples to which the image forming apparatus according to the first embodiment is applied; 
         FIG. 9  is a flowchart for explaining an operation example of an image forming apparatus according to a second embodiment; 
         FIG. 10  is a diagram of examples of an original document, a first image, and a second image in a second embodiment; 
         FIG. 11  is a flowchart for explaining an operation example of an image forming apparatus according to the second embodiment in the case of acquisition of a page description language; 
         FIG. 12  is a diagram for explaining an operation example of the image forming apparatus according to the second embodiment; 
         FIG. 13  is a diagram of an example of a PDL written when a PC according to the second embodiment determines keywords; and 
         FIG. 14  is a diagram for explaining an operation example of the PC according to the second embodiment in the case of using of a sheet having a watermark. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an image forming apparatus includes: an input section configured to input information to be printed; a first printing section configured to perform printing with a toner unerasable by an erasing device; a second printing section configured to perform printing with a toner erasable by the erasing device; and a control section configured to control the image forming apparatus to print, using the first printing section, at least a keyword stored in a storing section in advance among the information to be printed input by the input section and control the image forming apparatus to print, using the second printing section, information not printed by the first printing section. 
     In embodiments explained below, an image forming system is explained that determines whether a keyword such as “company secret” is present in an original document. In a first embodiment, an image forming system is explained that prints, if a keyword is detected, an entire page including the keyword with an unerasable toner and prints, if a keyword is not detected, the entire page with an erasable toner. In a second embodiment, an image forming system is explained that prints a keyword such as “company secret” and an area including the keyword with an unerasable toner and prints other areas of a page with an erasable toner. 
     First Embodiment 
       FIG. 1  is a diagram of an example of a system configuration of a first embodiment. An image forming system  500  includes an image forming apparatus  100 , which is an MFP (Multifunction Peripheral), having a copying function, a printer function, a scanner function, and a transmitting and receiving function for facsimile and email and a PC (Personal Computer)  200 , which is an information processing apparatus, used by a user. The image forming apparatus  100  and the PC  200  are connected by a LAN (Local Area Network)  300  and can communicate with each other. 
     The image forming apparatus  100  includes a control board  800  configured to collectively control hardware devices in the apparatus. The control board  800  includes a processor  801 , which is an arithmetic processing unit, such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The control board  800  includes a memory  802  including a RAM (Random Access Memory), which is a volatile storage device, and a ROM (Read Only Memory) and a HDD (Hard Disk Drive), which are nonvolatile storage devices. Further, the control board  800  includes a NIC (Network Interface Card)  803  configured to control communication with the outside. 
     The image forming apparatus  100  includes a control panel  810  including a keyboard  812  configured to receive an instruction from a user and a touch panel display  811  configured to display control contents and receive an instruction from the user. 
     A hardware configuration of the PC  200  is the same as that of an existing PC. The PC  200  includes a processor  204 , a memory  205 , and a NIC  206 . Further, the PC  200  includes a keyboard  202  and a mouse  203  configured receive an input from the user and a monitor  201  configured to display an image to the user. The NIC  803  and the NIC  206  perform control of communication with each other via the LAN  300 . 
     A schematic configuration of the image forming apparatus  100  is shown in  FIG. 2 . The image forming apparatus  100  can perform printing with two kinds of toners, i.e., a toner erasable by an erasing device and a toner unerasable by the erasing device. 
     The image forming apparatus  100  includes two input sections, i.e., an I/F section  10  (I/F: Interface) connected to the PC  200  through the LAN  300  and connected to a USB (Universal Serial Bus) memory and a scanner section  11  configured to read a document image. The image forming apparatus  100  includes a display operation section  12  for the user to perform various kinds of operation and a control section  13  configured to manage the control of the entire image forming apparatus  100 . The image forming apparatus  100  includes a storing section  14  configured to store a control program, data, and the like. The image forming apparatus  100  includes an image processing section  15  configured to apply various kinds of image processing such as gradation correction and edge detection processing to data to be printed acquired by the I/F section  10  and the scanner section  11 . The image processing section  15  is mounted as an ASIC (Application Specific Integrated Circuit). 
     The image forming apparatus  100  includes a first printing section  16  configured to form an image on a sheet with a toner unerasable by an erasing device used by the user (an erasing device  400 ) and a second printing section  17  configured to form an image on a sheet with a toner erasable by the erasing device  400 . Each of the first printing section  16  and the second printing section  17  includes photoconductive drums configured to perform printing with toners of four colors, cyan, magenta, yellow, and black. The photoconductive drums are individually arranged in a sheet conveying direction. 
     The control section  13  corresponds to the processor  801  and the storing section  14  corresponds to the memory  802 . The display operation section  12  corresponds to the control panel  810 . The I/F section  10  includes the NIC  803 . The control section  13 , the memory  802 , and the I/F section  10  are mounted on the control board  800 . 
     The operations of the image forming apparatus  100  are explained below. In the following explanation of the operations, first, an example in which a document image is read by the scanner section  11  and image data of the document image is processed is explained. Subsequently, an example in which data of a page description language is acquired from the PC  200  and the page description language is processed is explained. 
     First, an operation example of the image forming apparatus  100  in the case of reading of an original document with the scanner section  11  is shown in a flowchart of  FIG. 3 . Respective kinds of processing by the control section  13  in the flowchart explained below are realized by the control section  13  executing an arithmetic operation of a computer program introduced in the storing section  14  in advance and the control section  13  causing the storing section  14  to store data. 
     The control section  13  receives the input of a read input image from the scanner section  11  (ACT  1 ). The control section  13  determines whether a keyword registered in advance is present in the input image (ACT  2 ). 
     A determination method in ACT  2  is explained. First, the control section  13  executes a layout analysis and extracts a character string. As a layout analysis technique, a publicly-known technique can be used. The control section  13  extracts a character string present in a header or a footer in a document image. The control section  13  limits, for example, character strings extracted from the original document to a character string having a Y coordinate equal to or smaller than a certain threshold or equal to or larger than the threshold to regard the character string as the header or the footer. 
     Subsequently, the control section  13  executes processing by an OCR (Optical Character Reader) on the extracted character string and recognizes the character string. Finally, the control section  13  determines whether the recognized character string coincides with a registered character string stored in the storing section  14  in advance. If the character strings coincide with each other, the control section  13  determines that a keyword is present. 
     If an image pattern (e.g., a logo or a seal of a company) is registered in the storing section  14  as a keyword, the control section  13  determines whether an image pattern registered in advance is present on an input image using a pattern matching technique (a publicly-known technique can be used as the pattern matching technique). Further, an implementation may be adopted in which the control section  13  determines presence or absence of a keyword from a character string obtained as a result of reading and decoding a barcode (a one-dimensional barcode or a two-dimensional barcode) on an original document. 
     Referring back to the flowchart of  FIG. 3 , if the control section  13  determines that a keyword is absent in the determination in ACT  2  (No in ACT  3 ), the control section  13  controls the second printing section  17  to print an image to be processed such that the image is erasable by the erasing device  400  (ACT  5 ). On the other hand, if the control section  13  determines that a keyword is present (Yes in ACT  3 ), the control section  13  controls the first printing section  16  to print an image to be processed such that the image is unerasable by the erasing device  400  (ACT  4 ). 
     Thereafter, a sheet is fed from a paper feeding cassette to a transfer section and a toner is deposited on the sheet according to an input image signal. 
     If printing of all pages does not end (NO in ACT  6 ), the processing proceeds to ACT  1 . 
     In this embodiment, each of the first printing section  16  and the second printing section  17  includes photoconductive units for the respective colors. However, for example, there is also a configuration in which the first printing section  16  and the second printing section  17  share one set of photoconductive drums (for cyan, magenta, yellow, and black). As the control method in ACTS  4  and  5  in this configuration, if the image is printed with an erasable toner, the toner is supplied to the photoconductive drums from a toner cartridge for the erasable toner. If the image is printed with an unerasable toner, the toner is supplied to the photoconductive drums from a toner cartridge in which the unerasable toner is stored. 
     In the above explanation, the control section  13  determines presence or absence of a keyword. However, not only the control section  13  but also the image processing section  15  can perform the keyword determination. 
     A detection target is not limited to a keyword and may be a mark such as a seal, a one-dimensional barcode, and a two-dimensional code represented by a QR code. The detection target may be a watermark such as a background pattern shown in  FIG. 4A  and a woven pattern print that appears on a copied or scanned print. 
     In the above explanation, the control section  13  determines presence or absence of a keyword for each page and performs, for each page, control concerning with which of the unerasable toner and the erasable toner an image is printed. However, for example, it is conceivable that, if a keyword is present in an arbitrary page, all the following pages are printed with the unerasable toner. Alternatively, an implementation is also conceivable in which input images of all pages are stored in the storing section  14  and, if it is determined that a keyword is present in at least one page, all the pages are printed with the unerasable toner and, if a keyword is absent, all the pages are printed with the erasable toner. 
     An example in which the PC  200  converts image data to be printed into a page description language (hereinafter referred to as PDL) and prints the image data on the basis of the PDL is explained with reference to a flowchart of  FIG. 5 . 
     The control section  13  receives, through the I/F section  10 , the input of a PDL generated by a printer driver of the PC  200  (ACT  11 ). Subsequently, the control section  13  clears flag data (hereinafter simply referred to as flag) stored in the storing section  14  to  0  (ACT  12 ). The flag is information indicating whether a specific keyword is present in a page (one page) to be processed. 
     The control section  13  executes RIP processing and interprets a rendering command in the PDL (ACT  13 ). An example of the PDL is shown in  FIG. 6A . The PDL in this embodiment is divided into two parts, i.e., meta data in which information concerning an entire printing target such as “2-in-1 printing” or “duplex printing” is defined and a rendering portion in which information concerning respective rendering commands is defined. The rendering command is prepared for each object and includes definition information in printing of objects such as an arrangement, a size, and a color. As the rendering commands, three commands are set: a character command concerning characters, a figure command concerning a figure, and an image command concerning an image. In ACT  13 , the processing is performed in the order explained below. 
     The control section  13  acquires, for each command, a rendering command in the PDL. 
     The control section  13  acquires properties delimited by delimiters (in this example, “/” characters) in the acquired rendering command. If the object is the figure command such as “circle” or “rectangle” or the image command (a command head character string is “image”), properties such as a color and a size are acquired. If the object is the character command, properties such as a code, a font size, a color, and a font type of the character string are acquired. 
     The control section  13  determines whether a flag is set (whether the flag is a value other than 0) (ACT  14 ). If the flag is set (Yes in ACT  14 ), the processing jumps to ACT  18 . 
     If the flag is not set (No in ACT  14 ), the control section  13  determines whether a specific keyword is present in the rendering command (ACT  15 ). 
     The processing in ACT  15  is explained. If the rendering command is the character command, the control section  13  acquires a character string code in the properties after interpreting the character command and determines whether the character string is a registered keyword. If the rendering command is the figure command or the image command, the control section  13  once creates the figure or the image on the basis of the properties and carries out pattern matching with an image pattern in the same manner as explained above. 
     If a keyword is absent (No in ACT  16 ), the processing proceeds to ACT  18 . If a keyword is present (Yes in ACT  16 ), the control section  13  sets a flag (sets the flag to a value other than 0). 
     The control section  13  executes rendering processing according to the rendering command and renders a raster image (ACT  18 ). An example of the raster image created in ACT  18  is shown in  FIG. 6B . 
     The control section  13  renders raster images respectively according to the rendering commands and determines whether interpretation of all the rendering commands in the page ends (Act  19 ). If the processing is not completed for all the rendering commands in the page (No in ACT  19 ), the processing returns to ACT  13 . If the processing is completed (Yes in ACT  19 ), the control section  13  determines whether a flag is set (ACT  20 ). 
     If the flag is set (Yes in ACT  20 ), since the page includes a designated keyword, the control section  13  controls the image forming apparatus  100  to print the entire page with the unerasable toner, i.e., controls the image forming apparatus  100  to print the page using the first printing section. Conversely, if a flag is not set (No in ACT  20 ), since a designated keyword is not included, the control section  13  controls the image forming apparatus  100  to print the entire page with the erasable toner, i.e., controls the image forming apparatus to print the page using the second printing section (ACT  22 ). This control method is the same as ACTS  4  and  5  explained above. 
     If the processing for all the pages does not end (No in ACT  23 ), the processing returns to ACT  12  and processing for the next page is continued. 
     In this example, the flag is cleared during the start of processing for each page. However, if the flag is not cleared (i.e., in the case of NO in ACT  23 , the processing is returned to ACT  13 ), it is also possible to print, if a keyword appears in an arbitrary page, all the following pages with the unerasable toner. If the raster image is once stored in a storage device and is printed after the determination of presence or absence of a keyword in all the pages ends, it is also possible to print all the pages with the unerasable toner or the erasable toner. In other words, if a keyword is present, all the pages are printed by the first printing section  16 . If a keyword is absent, all the pages are printed by the second printing section  17 . 
     A form in the past and a form in the first embodiment are compared.  FIG. 7  is a diagram for explaining a problem in the past. In a situation shown in the figure, an original document including confidential information is printed (or copied) with the toner erasable by the erasing device  400  and a printed sheet is erased by the erasing device  400  to reuse the sheet. Immediately after the erasing, no image is formed on the sheet. If the sheet is reused for other purposes, it is likely that the sheet passes into others&#39; hands. If the sheet passes into others&#39; hand, thereafter, if the sheet is placed under an environment such as a low-temperature environment, it is likely that the erased toner develops a color again and the confidential information flows out to outside the company. 
       FIG. 8A  is a diagram of a form in the case of printing of confidential information using the image forming apparatus  100 . The image forming apparatus  100  prints the confidential information using the toner unerasable by the erasing device  400 , even if the user attempts to erase a sheet using the erasing device  400 , printed contents are not erased. Therefore, since the user can visually recognize that the confidential information is written on the sheet, it is possible to prevent the confidential information from flowing out to outside the company. 
     On the other hand, concerning a sheet not including confidential information as shown in  FIG. 8B , since the toner erasable by the erasing device  400  is used, printed contents are erased by the erasing device  400  and the sheet can be reused. 
     With the configuration of this embodiment, when electronic data including confidential information is printed, the entire page is printed with the unerasable toner. In the example in which the PDL is used, since presence or absence of a keyword can be determined by an analysis of a command rather than character recognition processing (OCR processing), a risk of erroneous determination is small. Consequently, it is possible to reduce a risk of a sheet having confidential information recorded thereon flowing out to outside the company because of carelessness of the user to cause leakage of the confidential information. 
     Second Embodiment 
     In a second embodiment, an implementation for printing only a keyword and an area including the keyword with an unerasable toner and printing areas other than the keyword and the area including the keyword using an erasable toner is explained. The configuration of an image forming system and the configurations of a PC and an image forming apparatus are the same as those in the first embodiment. Therefore, explanation of the configurations is omitted. 
     An operation example of the image forming apparatus  100  according to the second embodiment is explained. In the following explanation of operations, as in the first embodiment, first, an example in which a document image is read by the scanner section  11  and the image data is processed is explained. Subsequently, an example in which a PDL is acquired from the PC  200  and the PDL is processed is explained. 
       FIG. 9  is a flowchart for explaining an operation example of the image forming apparatus  100  according to the second embodiment in the case of reading of a document image with the scanner section  11 . 
     The control section  13  receives the input of a read input image from the scanner section  11  (ACT  31 ), copies the input image, and creates a second image (ACT  32 ). The control section  13  executes a layout analysis on the input image, slices characters, a figure, or an image from a header section or a footer section of the input image, and creates partial images (ACT  33 ). As a layout analysis technique, a publicly-known technique can be used. 
     The control section  13  determines whether the partial images are keywords registered in advance (ACT  34 ). Details of a determination method in ACT  34  are as explained below. 
     If a partial image is a character image, the control section  13  executes OCR processing and recognizes a character string. If the recognized character string coincides with a character string stored in the storing section  14  in advance, the control section  13  determines that the partial image is a keyword. If an image pattern (e.g., a logo or a seal of a company) is registered as a keyword, the control section  13  determines whether an image pattern registered in advance is present on an input image using a pattern matching technique (a publicly-known technique can be used as the pattern matching technique). 
     Further, it is also conceivable to determine presence or absence of a keyword from a character string obtained as a result of reading and decoding a barcode (a one-dimensional barcode or a two-dimensional barcode) on an original document as in the first embodiment. 
     Processing in the next ACTS  35  and  36  is executed on the partial image determined as the keyword. 
     The control section  13  arranges the partial image in a first image in a position and a size (width and height) same as a position and a size of the partial image arranged in the input image (ACT  35 ). The first image is image data in which nothing is drawn in an initial state. The control section  13  paints out, in white, the position where the partial image is arranged in the second image (ACT  36 ). 
     If the processing in ACTS  32  to  36  does not end for all the partial images (No in ACT  37 ), the processing is repeatedly executed on all the partial images. 
     An example of the first image and the second image created in this way is shown in  FIG. 10 . An area including a keyword such as “company secret” on an original image is drawn on the first image. On the other hand, on the second image, the partial images other than the area of the keyword are rendered and the area including the keyword is painted out in white. 
     The control section  13  controls the first printing section  16  to print the first image (ACT  38 ) and controls the second printing section  17  to print the second image (ACT  39 ). In this way, the first image including the keyword is printed with the unerasable toner and the second image not including the keyword is printed with the erasable toner. 
     A specific control method performed when only one set of photoconductive drums (for cyan, magenta, yellow, and black) are provided is explained below. Operations explained below are performed on the basis of the control by the control section  13 . 
     1. The unerasable toner is supplied to the photoconductive drums from a toner cartridge for the unerasable toner. 
     2. A sheet is fed from a paper feeding cassette to a transfer section. The unerasable toner is deposited on the sheet according to the first image. 
     3. The sheet on which the unerasable toner is deposited is not discharged at the present point. The erasable toner is supplied to the photoconductive drums. 
     4. The erasable toner is deposited on the sheet according to the second image. 
     5. The sheet on which the unerasable and erasable toners are deposited is discharged. 
     If printing of all pages does not end (No in ACT  40 ), the processing in ACTS  32  to  39  is executed until the printing of all the pages is completed. 
     By adopting such a configuration, as in the first embodiment, it is possible to reduce a risk of confidential information copied with the erasable toner flowing out to outside the company because of carelessness of a user to cause leakage of the confidential information. Since areas of a sheet other than a keyword indicating a confidentiality level (e.g., “company secret” or “department secret”) are erased, if a document having the same confidentiality level is printed, the sheet can be recycled and reused. 
     Subsequently, an operation example of the image forming apparatus  100  in the case of acquisition of a PDL from the PC  200  and applying of printing control to the acquired PDL is shown in a flowchart of  FIG. 11 . 
     The control section  13  receives, through the I/F  10 , the input of a page description language (PDL) generated by the printer driver of the PC  200  (ACT  51 ). 
     The control section  13  executes RIP processing and interprets rendering commands in the PDL (ACT  52 ). The control section  13  renders each of the rendering commands in a first image (raster image) not to be erased or a second image (raster image) to be erased (ACTS  53  to  56 ). 
     Processing in ACTS  53  to  56  is explained with reference to  FIG. 12  as well.  FIG. 12  is a diagram of examples of original image data, a PDL, a first image, and a second image generated in the processing. 
     If a rendering command is a character command, the control section  13  interprets the character command, checks a character code, and determines whether the character code is a registered keyword (ACT  53 ). If the character code is a registered keyword (Yes in ACT  54 ), the control section  13  renders the character code in the first image (ACT  55 ). If the character code is not a registered keyword (No in ACT  54 ), the control section  13  renders the character code in the second image (ACT  56 ). 
     Concerning a figure command or an image command, as in the first embodiment, the control section  13  carries out pattern matching with an image pattern to determine whether a figure or an image is a keyword (ACT  53 ). If the control section  13  determines that the target rendering command indicates a registered image pattern (Yes in ACT  54 ), the control section  13  renders an image as a result of interpreting the rendering command in the first image not to be erased (ACT  55 ). If the control section  13  determines that the target rendering command does not indicate a registered image pattern (No in ACT  54 ), the control section  13  renders the image in the second image to be erased (ACT  56 ). 
     However, in the related art, if images are drawn one on top of the other on the same pixel, only the image drawn after the image drawn earlier is erased is drawn. However, in the image forming apparatus, if objects are drawn one on top of the other in the same manner as the related art, it is likely that an important keyword such as “company secret” or “confidential” cannot be read if an image after printing is erased. Therefore, only if the first image not to be erased is drawn earlier in the same pixel position as the second image to be erased, pixels on the second image are replaced with white pixels. On the other hand, pixels on the first image are not replaced with white pixels. Consequently, the important keyword is surely printed with the unerasable toner while chances of the unerasable toner and the erasable toner being ejected in the same position on a sheet are reduced. 
     If the processing does not end for all the rendering commands in the same page (No in ACT  57 ), the processing is repeatedly executed on all the rendering commands. 
     The control section  13  controls the image forming apparatus  100  to print the first image with the unerasable toner (ACT  58 ) and print the second image with the erasable toner (ACT  59 ). In other words, the control section  13  controls the image forming apparatus to print the first image using the first printing section  16  and controls the image forming apparatus to print the second image using the second printing section  17 . A control method is as explained above. 
     If a page currently being processed is not the last page (No in ACT  60 ), the processing returns to ACT  52 . 
     In the example explained above, if the control section  13  of the image forming apparatus  100  performs interpretation and rendering of the rendering commands of the PDL as RIP, the control section  13  determines whether rendered characters and images should be printed with the unerasable toner or should be printed with the erasable toner. However, this determination can also be realized by the processor  204  of the PC  200  executing an arithmetic operation of a computer program of the printer driver. Specifically, if the processor  204  (the printer driver) of the PC  200  generates a PDL on the basis of electronic image data (GDI) output from an application, the processor interprets font data in the GDI, determines whether the font data is a keyword stored in the memory  205  in advance, and generates a PDL in which a symbol indicating which of the erasable toner and the unerasable toner is used is embedded. 
     A series of operations of the PC  200  are explained. The processor  204  of the PC  200  acquires an object in electronic data created by applications. The object is a font data of a character string in the case of character string information and is a raster image in the case of image data or figure data. The processor  204  acquires one or plural keywords stored beforehand from the memory  205  and determines whether the object is a keyword. In the case of the character string, the processor  204  determines whether a code coincides with a keyword or the object includes a code. In the case of the image or figure data, the processor  204  performs the determination using the pattern matching processing as described above. If the object is a keyword, the processor  204  gives, for example, a symbol of “unerasable toner” to the object and creates a rendering command. On the other hand, if the object is not a keyword, the processor  204  gives, for example, a symbol of “erasable toner” to the object and creates a rendering command. The processor  204  transmits the PDL created in this way to the image forming apparatus  100  as information to be printed. 
     An example of the PDL created by the PC  200  is shown in  FIG. 13 . The PDL shown in  FIG. 13  is a PDL converted from the document data shown in  FIG. 12  by the PC  200 . The control section  13  of the image forming apparatus  100  acquires symbols included in the rendering commands to perform control concerning with which toner printing is performed. Specifically, the control section  13  renders a rendering object including the symbol of “unerasable toner” in the first image and controls the first printing section  16  to print the first image. The control section  13  renders a rendering object including the symbol of “erasable toner” in the second image and controls the second printing section  17  to print the second image. 
     An implementation is also conceivable in which the processor  204  of the PC  200  determines whether a specific sheet having a watermark such as “strictly confidential” or “company secret” is selected or whether a specific mode such as woven pattern printing is selected rather than determining only a keyword in an original document, whereby the control section of the image forming apparatus  100  performs control concerning with which of the erasable toner and the unerasable toner printing is performed. This implementation is explained with reference to  FIG. 14 . The processor  204  of the PC  200  adds a symbol for designating the erasable toner to an object (an original document shown in  FIG. 14 ) of electronic data (GDI) output by an application and adds a symbol for designating the unerasable toner to an object for printing a watermark, a woven pattern, or the like registered in advance in the PC  200  (the printer driver). 
     The printing order of the first printing section  16  and the second printing section  17  is not limited to this. 
     In the above explanation, the control section  13  determines presence or absence of a keyword for each page and performs control concerning with which of the unerasable toner and the erasable toner an image is printed. However, for example, it is conceivable that, if a keyword is present in a certain page, the first image not to be erased of the page is stored in the storing section  14  and, if a keyword is absent in the following pages, i.e., if the following pages are pages in which the first image is a totally white image, the stored first image is treated as the first image of the following pages and printed with the unerasable toner. By adopting such an implementation, the keyword is printed with the unerasable toner on the page following the page in which the keyword is present. 
     It is also conceivable that the first images and the second images of all the pages are stored in the storing section  14  and, if it is determined that a keyword is present in at least one page, the first image of the page in which the keyword is present is printed with the unerasable toner on a page in which a keyword is absent and the first image is a totally white image. By adopting such an implementation, concerning a job including a keyword, the keyword is printed with the unerasable toner on all pages. 
     By adopting the configuration of this embodiment, as in the first embodiment, it is possible to reduce leakage of information due to carelessness of the user. Further, since areas of a sheet other than a keyword indicating a confidentiality level (e.g., “company secret” or “department secret”) are erased, if a document having the same confidentiality level is printed, the sheet can be recycled and reused. 
     Further, if a PDL is used, it is possible to control printing according to a designated symbol without determining whether the image forming apparatus  100  performs printing in which of the printing sections. Therefore, it is possible to reduce a risk of erroneous identification. 
     The toners in the first and second embodiments include not only toners for obtaining hard copies in a multifunction peripheral, a facsimile, a copying machine, and a printer but also recording and display materials such as printing ink, a printing ribbon, and inkjet ink. 
     As explained above in detail, according to the technique described in this specification, a keyword of confidentiality information is printed with the unerasable toner. Therefore, it is possible to reduce a mistake of the user leaking confidential information without noticing that the confidential information is printed. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.