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Application of Adobe® Photoshop® CC 2018 for Identifying the Source of HP® Color Laser Printouts

Abstract In today’s digital world, printer forensics is one of the most important disciplines to reveal the authenticity of printed documents and track criminals. Digital steganography is an advanced approach to secure color laser printing processes, but it cannot be applied to monochrome laser printers. Therefore, the identity of the machine used to print color questioned documents provides a valuable means for detecting forgery crimes in digital forensic labs and law enforcement agencies. Based on this, we introduced a new forensic method that unveils the steganography (hidden information) embedded in color laser printouts via an adopted preset in Adobe® Photoshop® CC 2018. This forensic tool can be applied as a nondestructive and indirect tool for image processing. In the present work, printing, scanning, extraction, and measurements for the embedded tracking dots of candidate color laser printouts were conducted. Thirty-five HP® color laser printers were selected with different and same models with different serial numbers and used to print a hundred color laser printouts. The defined coded dots matrix patterns that characterized the color laser machines of the HP® brand could clearly be determined. Therefore, this procedure could successfully be applied to distinguish between various color laser printouts printed by HP® printers with a variant serial number in digital forensic labs with a conclusive accuracy ratio attained to one hundred percent.


Abstract
In today's digital world, printer forensics is one of the most important disciplines to reveal the authenticity of printed documents and track criminals. Digital steganography is an advanced approach to secure color laser printing processes, but it cannot be applied to monochrome laser printers. Therefore, the identity of the machine used to print color questioned documents provides a valuable means for detecting forgery crimes in digital forensic labs and law enforcement agencies. Based on this, we introduced a new forensic method that unveils the steganography (hidden information) embedded in color laser printouts via an adopted preset in Adobe ® Photoshop ® CC 2018. This forensic tool can be applied as a nondestructive and indirect tool for image processing. In the present work, printing, scanning, extraction, and measurements for the embedded tracking dots of candidate color laser printouts were conducted.
Thirty-five HP® color laser printers were selected with different and same models with different serial numbers and used to print a hundred color laser printouts.
The defined coded dots matrix patterns that characterized the color laser machines of the HP ® brand could clearly be determined.
Therefore, this procedure could successfully be applied to distinguish between various color laser printouts printed by HP ® printers with a variant serial number in digital forensic labs with a conclusive accuracy ratio attained to one hundred percent.

Printing and Sample Collection
White papers of A4 size were selected for printing color laser printouts. We collected the printouts from different work offices. In this study, we worked on the HP ® color laser machines. The details of the studied models are given in Table-1.

Introduction
Digital forensic science is a broad field that also encompasses the identification of the source of color laser printouts. Nowadays, there are various methods of identification. These methods can be divided into different categories: statistical analysis, halftone analysis, and noisy features analysis [1][2][3][4]. All these methods have provided good results in the identification of printout sources but have not achieved an accuracy ratio of 100%. Therefore, to prevent or combat the increasing rate of forgery via color laser printers such as invoices, money, tickets, fraud ID, and contracts and certificates, we need to identify the source of these color laser printouts with an acceptable accuracy ratio [3][4][5]. However, passive techniques aiming to use imperfections generated by optical, electrical, or mechanical defects in machines were not satisfactory when tested and did not enable detection with an acceptable accuracy ratio [5].
On the other hand, there is an active technique that aims to track extrinsic features embedded in color printouts of machines [6]. An active technique tracks features in the form of yellow dots. These yellow dots are called machine identification codes (MIC), counterfeit protection system (CPS) codes, and coded dots matrix (CDM) patterns [7].
The tracking dots are very small in size and cannot be seen by the naked eye [8]. The tracking of these yellow dots is the authorized source of information about color laser machines, such as serial number, model, and in special cases, the date and time of the printing processes. So bearing this in mind, we applied the active technique in our paper.
In our work in this paper, we presented a nondestructive and indirect technique by Adobe ® Photoshop ® CC 2018 in the RGB mode for image analysis to detect extrinsic features of color laser printouts. We studied one hundred color laser printouts from thirty HP ® color laser printers with the same and different models. The target goal in this study was achieved when we combined questioned color laser printouts with the defendant printer.

Materials and Methods
In this procedure, we followed the steps in Figure-

Sample Preparation
All printouts were scanned by a Cano Scan ® LIDE 120 at a resolution more than 800 dots per inch (DPI). Because of the nanosize of the coded dots matrix, the resolution was increased to an extent that yields more vivid images and enables easy extraction.

Extraction
In this step, we applied an indirect method to extract the coded dots matrix patterns (CDMP) for the candidate printouts as a soft copy (because a hard copy of the printouts was not used in the image processing technique). Adobe ® Photoshop ® CC 2018 was utilized as a tool for processing images. The RGB mode was selected to manipulate the scanned images.

Measurements
We measured all spaces around the basic coded dots matrix patterns of the undertaken printouts. We employed Adobe® Photoshop ® CC 2018 for all measurements with magnification at 100% relative to the basic images. Furthermore, live measurements were carried out directly on the color laser printouts by using a digital microscope and were calibrated with the estimated measurements.

Results and Discussion
In the current work, one hundred color printouts were printed by thirty-five HP ® color laser printers and multifunction machines, as shown in Table- We could successfully track and extract the tracking dots         (1,2,3,4, and 5) for the repeated basic patterns that exist horizontally and vertically of the coded dots matrix in an example of HP ® color laser jet 3600 sample.  that can be summarized as follows: 1. The interior distance between two adjacent dots of the basic coded dots matrix pattern was 0.0766 cm. These measurements can be seen in Figure-6.
Moreover, the distribution of the yellow tracking dots inside the coded dots matrix for each HP ® color laser printer did not change its position when we printed at variant intervals. We therefore determined that all the investigated HP ® color laser machines contain a constant code of information that only reveals the machine serial number and the model type and that neither the printing time or the date was encoded in these coded dots matrixes.

Conclusion
We could successfully track, extract, and measure the spatial distances of the security feature embedded in all the HP® color laser printouts investigated using the conclusive The basic unit of the tracking yellow dots that was repeated regularly was composed of sixteen columns and twenty rows in a regular grid pattern with a unique and different distribution of yellow tracking dots inside them. We figured out each color laser printer or multifunction printer studied had the same first five rows that represented the identity of HP ® brand but had its unique distribution of the tracking dots after the fifth row inside the coded dots matrix pattern. The coded dots matrix patterns of HP ® printers are regular in their shapes and represented only the serial number with no information about the date or the time of the printing processes.
Therefore, in the current study, we presented a conclusive forensic technique for determining the printout sources of HP ® color laser printers that distinguish between two or more color laser HP ® printouts with a conclusive accuracy of one hundred percent.