A document that one does not consider important may contain invaluable information to others. Every single person engaged in business activities faces the risk of confidential information leaking.
By medium, paper documents have always been the largest source of information leakage. Once prepared, documents are photocopied over and over again, which may lead to unexpected information leaking. Therefore, it is very important to prevent unauthorized photocopying. Information can be effectively managed by employing functions that (i) prevent second-generation photocopying of documents with a “photocopying prohibited” message and (ii) enable photocopying only when a preset password is entered.
Konica Minolta developed a security watermark function to embed photocopy protection data into printouts for information management.
If a document is photocopied or printed using this security function, the printout bears a security watermark pattern in the background. If one tries to photocopy this printout, the MFP detects the embedded security watermark pattern. The photocopying job is stopped (the photocopy protection function), or a password input screen appears requiring a user to enter a correct password before resuming photocopying (the password-protected photocopying function).
Four types of tiny symbols (i.e. large/small dots (•) and dashes (–)) are used in security watermark patterns to make the photocopy protection data less visible. Multiple sets of pattern data are embedded so that the data can be restored even if part of a document is falsified or damaged.
Security watermark pattern
4 types of symbols
※These functions are effective only with MFP models equipped with Konica Minolta’s security watermark functions. An optional security kit is required.
To prevent unauthorized reproduction of documents, the MFP must be capable of (i) detecting the data embedded in the watermark pattern while scanning the document after the start button is pressed and (ii) completing data analysis before printing is started. To reduce the time required for detecting and analyzing the security data, Konica Minolta succeeded in hardware implementation of the algorithm and increased processing efficiency. Here, “hardware implementation” refers to a technology to divide a set of algorithms into simple blocks (exclusively used for processing), process these blocks one after another, and thereby increase speed.
To achieve hardware implementation, the symbol detection and data analysis algorithm had to be rendered compact. Konica Minolta’s accomplishments derived from image processing algorithm research were utilized to achieve this goal. The algorithm has been simplified based primarily on the three solutions below.
- Employing a common detection and processing sequence for the “photocopy protection function” and “password-protected photocopying function” from the beginning to a certain point: Overlapping operations have been avoided.
- Processing the symbols with low resolution to reduce the number of pixels: The number of operations has been halved.
- Performing binary coded processing of the symbols (converting the gray area into white or black): The number of operations for analysis has been reduced.
When photocopying a document, the orientation (top/bottom/left/right) of the document is not always the same. The security data must be detected accurately in any orientation. Multiple sets of alignment pattern data are embedded in the watermark pattern so that the pattern can be detected from multiple points. A histogram-based cumulative analysis is performed to determine the orientation of the security data. CRC (cyclic redundancy check)-based error checks are performed to enhance the analysis precision and reliably determine the orientation.