Research on detection techniques for pattern modifications of playing cards used in illegal gambling operations.

We investigated pattern-modified marked cards used in fraudulent gambling cases in Korea. These cards are printed with modifications to some of the repeated marks on the back, revealing the hand on the front and enabling fraudsters to deceive their victims. We proposed a method for identifying the modified part by first enhancing the card's color difference using an image processing technique and then calculating the similarity between the repeated basic patterns with a Siamese network. This method is fast and convenient, as it can determine the deformation with only 1 or 2 cards and can be implemented in mobile applications, allowing law enforcement officers to investigate quickly. The proposed method serves as a useful tool to aid document examiners in making judgments, as it does not require expensive equipment and effectively visualizes the alterations.

Identification of document paper using hybrid feature extraction.

Document forgery is a significant issue in Korea, with around ten thousand cases reported every year. Analyzing paper plays a crucial role in examining questionable documents such as marketable securities and contracts, which can aid in solving criminal cases of document forgery. Paper analysis can also provide essential insights in other types of criminal cases, serving as an important clue for solving cases such as the source of a blackmail letter. The papermaking process generates distinct forming fabric marks and formations, which are critical features for paper classification. These characteristics are observable under transmitted light and are created by the forming fabric pattern and the distribution of pulp fibers, respectively. In this study, we propose a novel approach for paper identification based on hybrid features. This method combines texture features extracted from images converted using the gray-level co-occurrence matrix (GLCM) approach and a convolutional neural network (CNN), with another set of features extracted by the CNN using the same images as input. We applied the proposed method to classification tasks for seven major paper brands available in the Korean market, achieving an accuracy of 97.66%. The results confirm the applicability of this method for visually inspecting paper products and demonstrate its potential for assisting in solving criminal cases involving document forgery.

Detection of hidden marks on Hwatu cards used in illegal gambling.

Hwatu is a popular card game widely played in both Korea and Japan. This study examined hwatu cards used in the fraudulent gambling in Korea. Fraudsters used the hwatu cards, with hidden marks printed on the back using special ink to identify the cards so that they could deceive unknowing game players. These marks are invisible to the naked eye under normal conditions and are only visible when wearing special lenses. When suspicious hwatu cards are sent to the forensic laboratory, detection of the hidden mark conducted by the microscope, video spectral comparator (VSC), and radiography, which are laborious. In this study, we developed visualization of the hidden mark on the hwatu cards by utilizing a set of the algorisms including color splitting, histogram normalization, FFT denoising, These algorithms were applied to mobile applications affording convenience and accessibility to help prevent fraud or to help law enforcement conduct an immediate investigation. The proposed method was confirmed to be simple and effective in detecting hidden marks on hwatu cards without the need for costly equipment.

A waterproof cellulose nanofibril sheet prepared by the deposition of an alkyl ketene dimer on a controlled porous structure.

This study prepared a waterproof cellulose nanofibril (CNF) sheet via the deposition of an alkyl ketene dimer (AKD) on the sheet's controlled porous structure. The porosity of the CNF sheet was controlled by drying under different conditions, which included hot-press drying (HD) and solvent-exchange drying (SD), and the effect on the hydrophobization and water-related barrier performance of the sheet were investigated. When the SD sheet was immersed in an AKD wax solution, the sheet exhibited super-hydrophobicity and a lower water vapor transmission rate, compared with the HD sheet. This indicated that the porous structure of the SD sheet enabled AKD to be adsorbed on both the surface and the inner surface and it filled in the pores of the sheet, thereby giving rise to excellent waterproofing properties. The performance of a hydrophobized SD sheet as a water barrier material was comparable to a linear low-density polyethylene film. This study confirms the possibility for AKD wax to be immersed in a porous CNF sheet and used as a potential barrier material in hydrogel packaging.

Scanner model classification with characteristic brightness variations.

Analog documents and scanned digitized files are now considered equivalent in legal contexts, and the widespread supply of multi-functional printers has led to a surge in the use of scanned documents. With image editing tools, there has been more cases of forgery involving scanned files. This has highlighted the importance of integrity and authenticity verification of scanned documents submitted as court evidence. Extensive studies have been conducted on source scanner identification and detection of alteration in scanned documents. Past research usually relied on machine learning with Support Vector Machine (SVM) and Convolutional Neural Network (CNN), and was focused more on images rather than text documents. Brightness variations are produced depending on the repetitive arrangement and relative intensity of light sources, and such patterns can be clearly observed in scanned images by the Charged Coupled Device (CCD) type flatbed scanner. The separate image module of the Contact Image Sensor (CIS) also leads to characteristic brightness variations. To extract and enhance these brightness variations, image processing techniques such as separating color channel and adjusting gradation and contrast are applied. The proposed method was tested on five scanner models, and the results confirmed that each scanner had unique brightness variations. This study is the first to extract brightness variations as a unique characteristic of each scanner model and recognize the potential of brightness variations in source identification and manipulation detection. A major advantage is that brightness variations are physical, robust, and visible. The research will be expanded with multicolor documents, counterfeit documents, and text-independent detection.

A study on factors that affect error rates in handwriting examinations of Korean characters by forensic document examiners and non-experts.

Forensic handwriting examinations are often considered important in trials, and especially those related to property issues. There is also increasing demand by courts for the quantification of handwriting examination results. Notably, in forensic science, error rates in forensic handwriting examinations should be carefully quantified in order to ensure their reliability as evidence. The present study examined error rates in forensic handwriting examinations conducted by both forensic document examiners (FDEs) and non-experts. To this end, four FDEs affiliated with forensic science institutes and a group of 20 laypersons were asked to perform a forensic handwriting examination of Korean characters in various forms (long text, short text, and signature samples) in blind test settings; i.e., specific information about the test was not given. The test was composed of 180 questions. The results showed that the incorrect answers are much higher in the non-expert group than the expert group though; however, the percentage of "inconclusive opinion" answers was higher in the expert group. It was also found that, in the expert group, error rates could be lowered by allowing a joint examination (or a peer review) to be performed. Meanwhile, the expert group showed relatively high error rates when dealing with handwriting samples simulated or disguised, rather than those that contained a small number of characters, such as signature samples. In the non-expert group, financial reward did not contribute to increasing the correct answers (%) of handwriting examination but rather encouraged examiners not to choose "inconclusive opinion" answers. This result indicates that a financial reward may unintentionally affect the examination results. The major findings of the present study are of significance in that this study is the first attempt to specifically examine error rates in forensic handwriting examinations of Korean characters conducted by both expert and non-expert groups. This study also demonstrated that the exchange of opinions among FDEs affected the resultant error rates and overall examination results. It was also found that financial reward may affect handwriting examination results as well.

Incorporation of CNF with Different Charge Property into PVP Hydrogel and Its Characteristics.

Cellulose nanofibril (CNF)-added polyvinylpyrrolidone (PVP) hydrogels were prepared using different types of CNFs and their properties were investigated. CNFs with different morphology and surface charge properties were prepared through quaternization and carboxymethylation pretreatments. The quaternized CNF exhibited the narrow and uniform width, and higher viscoelastic property compared to untreated and carboxymethylated CNF. When CNF was incorporated to PVP hydrogel, gel contents of all hydrogels were similar, irrespective of CNF addition quantity or CNF type. However, the absorptivity of the hydrogels in a swelling medium increased by adding CNF. In particular, the quaternized CNF-added PVP hydrogel exhibited the highest swelling ability. Unlike that of hydrogels with untreated and carboxymethylated CNFs, the storage modulus of PVP hydrogels after swelling significantly increased with an increase in the content of the quaternized CNF. These indicate that a PVP hydrogel with a high absorptivity and storage modulus can be prepared by incorporating the proper type of CNF.

Preparation of Transparent and Thick CNF/Epoxy Composites by Controlling the Properties of Cellulose Nanofibrils.

Cellulose nanofibrils (CNFs) have been used as reinforcing elements in optically transparent composites by combination with polymer matrices. In this study, strong, optically transparent, and thick CNF/epoxy composites were prepared by immersing two or four layers of CNF sheets in epoxy resin. The morphology of the CNF, the preparation conditions of the CNF sheet, and the grammage and layer numbers of the CNF sheets were controlled. The solvent-exchanged CNF sheets resulted in the production of a composite with high transparency and low haze. The CNF with smaller width and less aggregated fibrils, which are achieved by carboxymethylation, and a high number of grinding passes are beneficial in the production of optically transparent CNF/epoxy composites. Both the grammage and number of stacked layers of sheets in a composite affected the optical and mechanical properties of the composite. A composite with a thickness of 450-800 µm was prepared by stacking two or four layers of CNF sheets in epoxy resin. As the number of stacked sheets increased, light transmittance was reduced and the haze increased. The CNF/epoxy composites with two layers of low grammage (20 g/m2) sheets exhibited high light transmittance (>90%) and low haze (<5%). In addition, the composites with the low grammage sheet had higher tensile strength and elastic modulus compared with neat epoxy and those with high grammage sheets.