The Role of the Slit Glass in a Photocopy System and Its Effect on Photocopied Documents

Forensic Document Examiners (FDE) are very familiar with print system defects. It is essential for an FDE to maintain their expertise and stay abreast of changes in printing technology which may have an impact on forensic examinations and comparisons. Print defects in a photocopy system are commonly referred to as trash marks, and can originate from various components of the device, such as the drum, platen or cover. These trash marks can be distinguishing and lead to a common source determination. Over time, there have been advances in digital photocopier technology which changed the configuration of the device. When the automatic document feeder (ADF) is utilized on a digital copier equipped with a slit glass, the platen glass is not involved in the copying process. In contrast to the traditional configuration of a stationary document and a moving imaging device, this system has a fixed imaging device while the document moves over the slit glass. This configuration has an impact on photocopier defects and their role in photocopy comparisons. This paper will discuss how the slit glass is utilized in the copying process and how and why defects will manifest themselves differently.