Four hundred color laser printout samples from 93 color laser printers and multifunction printers with the same and the different models as shown in Table 1 were investigated. After completing both the printing and scanning steps, we have unveiled the steganography form existing in all the color laser printouts undertaken in our study at the extracting step. Therefore, we figured out that all characteristic tracking dots were spread all over the printout samples in a specific coded of dot matrix patterns. Configurations, distributions, and the spatial distance measurements of these tracking dots were determined by the Adobe® Photoshop® CC 2018. We were able to track and extract successfully the yellow tracking dots printed in all color laser printout samples. The configuration and the distribution of the tracking yellow dots extracted from color laser printout samples of Ricoh® brand are characterized by the following aspects:
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All embedded tracking yellow dots onto the paper sheets were aligned in a uniform of horizontal rows and vertical columns patterns.
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The basic coded dot matrix pattern repeated regularly is composed of seven columns with eight rows of a defined coded dot matrix pattern.
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Basic coded dot matrix grouped vertically in 18 rows; each one of them contained 12 repeated basic coded dot matrix patterns.
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Basic coded dot matrix grouped horizontally of 12 columns; each one of them contained 18 repeated basic coded dot matrix patterns.
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On the upper left corner of the coded dot matrix pattern, there are two constant and adjacent dots, which are separated from another repeated one.
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There is a unique distribution of the yellow tracking dots inside the coded dot matrix pattern for each color laser printer or multifunction printer investigated.
The defined configuration of the coded dot matrix patterns for color laser printers of Ricoh® brand and their different distributions can be shown clearly in Figs. 4, 5, and 6 in both RGB and CMYK modes as viz.
Figure 4 exhibited the regular repeated basic coded dot matrix model between four constant separated dots, two of them at the upper left corner of the coded dot matrix model from the first row and the other two at the right lower of the last row and marked with two red ovals.
Furthermore, Fig. 5 represented two basic coded dot matrix patterns surrounded by red squares and separated from another one by two neighboring dots as starting dots for the basic pattern and marked with green ovals.
Moreover, Fig. 6 exhibits the CMYK mode for the yellow tracking dots that are grouped in the defined shape composed of seven columns and eight rows as given inside each blue rectangle. In addition, two of the starting dots are presented inside each red circle that separated each basic pattern. By comparison, in each basic coded dot matrix pattern in Figs. 4, 5, and 6, we could discriminate the difference in the distribution inside them but all contained the defined configuration of the coded dot matrix pattern composed of seven columns and eight rows.
To facilitate our illustration, we simulated the defined configuration of the regular repeated basic coded dot matrix pattern presented in one model of the color laser printouts of Ricoh® brand as an example to simplify and illustrate the following measurements as depicted in Figs. 7 and 8.
We measured all the spatial spaces surrounding the basic repeated coded dot matrix model embedded onto each color laser printout studied from all directions. The non-destructive and indirect tool of Adobe® Photoshop® CC 2018 was used with a custom preset after the calibration (Fig. 3). We found all color laser printouts studied had constant spatial distance measurements that can be summarized and given as viz:
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The spatial distance between two adjacent dots inside the basic coded dot matrix model = 0.1 cm.
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The width of the basic coded dot matrix model = 0.6 cm.
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The length of the basic coded dot matrix model = 0.7 cm.
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The horizontal spacial distance between two adjacent basic repeated coded dot matrix models in each row = 1 cm.
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The vertical distance between two adjacent basic repeated coded dot matrix models in each column = 0.9 cm.
These measurements can be visualized in Fig. 9.
Furthermore, we printed from the same and the different models of color laser machines of Ricoh® brand on interval times (every day, every month, and every year) but we found that each color laser printout sample did not change its unique distribution of the tracking yellow dots inside the basic coded dot matrix model. So, this means each colored laser machine of Ricoh® brand contains the coded constant information about the machine serial number and the model type only but did not contain information about the date nor the time of the printing processes.