Research on the Examination of Laser Printed Documents Using Coaxial Optical Techniques

This study investigates the method of using coaxial light to differentiate between laser printer and detect the addition of printed documents. Documents printed by laser printers of different brands and models are inspected using coaxial light, with the reflection of the printed text and graphics, specifically the degree of brightness or darkness, serving as a means to distinguish the printer models. The same method is used to inspect documents that have undergone additional printing on the same printer model as well as on different printer models, and the differences in the coaxial light response after the additional printing are analyzed. The experimental results show that the coaxial light response of documents printed by the same model in a single run and at different times remains basically stable, with minimal influence from paper quality and toner amount, making it a viable feature for differentiating laser printers. The coaxial light response varies significantly among documents printed by different models, with a high degree of differentiation; Moreover, the differences in the coaxial light response of the text and graphics in the added printed documents are even more pronounced, enhancing discrimination further. Overall, the study concludes that the coaxial light inspection method is a non-destructive, fast, and efficient method for forensic analysis of laser printed documents.