Spectral Data Analysis for Forgery Detection in Official Documents: A Network-Based Approach

Abstract

Despite the huge advances in digital communications in the last decade, physical documents are still the most common media for information transfer, especially in the official context. However, the readily available document processing devices and techniques (printers, scanners, etc.) facilitate the illegal manipulation or imitation of original documents by forgers. Therefore, verification of the authenticity and detection of forgery is of paramount importance to all agencies receiving printed documents. We suggest an unsupervised forgery detection framework that can distinguish whether a document is forged based on the spectroscopy of the document’s ink. The spectra of the tested documents inks (original and questioned) were obtained using laser-induced breakdown spectroscopy (LIBS) technology. Then, a correlation matrix of the spectra was calculated for both the original and questioned documents together, which were then transformed into an adjacency matrix aiming at converting it into a weighted network under the concept of graph theory. Clustering algorithms were then applied to the network to determine the number of clusters. The proposed approach was tested under a variety of scenarios and different types of printers (e.g., inkjet, laser, and photocopiers) as well as different kinds of papers. The findings show that the proposed approach provided a high rate of accuracy in identifying forged documents and a high detection speed. It also provides a visual output that is easily interpretable to the non-expert, which provides great flexibility for real-world application.

A Review of Laser-Induced Breakdown Spectroscopy (LIBS) for Document Examination: Fundamentals, Mechanism, and Application

“…Optimizing the parameters for LIBS measurements requires a comprehensive understanding of LIBS plasma physics and consideration of environmental factors that may affect the plasma lifetime and features [39]. The plasma lifetime stages are depicted in Figures 2(a) and 2(b) [39,45]. Figure 2(a) presents an overview of the plasma lifetime, which is divided into three stages (labelled as i, ii, and iii), whereas Figure 2(b) provides a more detailed explanation of each stage, appropriately labelled with the corresponding stages.…”

“…Furthermore, the recombination of electrons and ions in this stage is essential for generating line emission, which impacts the radiation processes [41]. (i, ii, and iii) and (b) detailed explanation of these stages [39,45] As the plasma continues to expand and cool after ignition, there is a concurrent change in electron temperature and density. During this process, electrons transition to lower energy levels and the electrons emits photons in the decay.…”

“…Al-Ameri et al [45] proposed an unsupervised clustering algorithm inspired by the DBSCAN algorithm (density-based spatial clustering of applications with noise). Their research primarily focused on developing the algorithm and they did not provide details on the elemental profiles of the samples in their study.…”

“…Figure 2. Schematic diagram of plasma lifetime stages; (a) an overview of plasma lifetime stages(i, ii, and iii) and (b) detailed explanation of these stages[39,45] …”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…A further paper that assessed the veracity of documents was presented by Al-Ameri et al who used LIBS to analyse the inks followed by a chemometric approach to analyse the data . 298 A correlation matrix of the spectra was calculated for both the original and questioned documents together. This was then transformed into an adjacency matrix with the aim of converting it into a weighted network under the concept of graph theory.…”