Patent ID: 7628555

Claim:
An image forming apparatus comprising: a manuscript table; a scanner being configured to scan an original image on a sheet of printing paper placed on the manuscript table; an electric tag reader being arranged on the manuscript table; a paper feeding tray stocking one or more sheets of printing paper; a printing unit being configured to print an image on a sheet of printing paper; a paper feeder being configured to feed the printing paper to the printing unit and to discharge the printing paper with the printed image to a discharge tray; an electric tag writer being arranged on a paper carrier path; an inputting unit being arranged to allow a user to input a decoding key; and a controller switching between a coding mode and a decoding mode, in the coding mode, the controller converting image data into coded data with a code string using a coding key, making the printing unit form a small pattern string on a sheet of printing paper by printing small patterns on the printing paper, the small patterns being printed on the sheet of printing paper, the small patterns having coded shapes being different from shapes of the original image, and making the electric tag writer record the coding key or data corresponding to the coding key in a recording medium combined with the printing paper, each small pattern corresponding to a code constructing the coded data, and in the decoding mode, the controller making the electric tag reader read out recorded data from the recording medium, determining whether the decoding key inputted from the inputting unit corresponds with the recorded data read out from the recording medium, making the scanner scan the small pattern string recorded on the printing paper when the decoding key inputted from the inputting unit corresponds with the recoded data read out from the recording medium, converting the small pattern string scanned from the printing paper into the code string, decoding the code string into the original image data using the decoding key, and making the printing unit print the original image on a sheet of printing paper based on the image data.