Digital imaging examines laser-printed documents: Off-the-shelf components and custom algorithms perform forensic analysis of print used in crime.

<p>The article shows that the length of printed graphical objects and text characters is dependent on their position on a page and the printing machine used. The paper describes how this was quantified using digital image analysis and explains how the technology can be used to forensically examine printed documents. </p>

<p>The work is described from a systems integration perspective. It describes both the individual hardware and software components and demonstrates how they can be combined to make a complete digital imaging system. It also explains how the algorithm was developed to overcome hardware limitations and to make the required measurements. The limitations overcome were noise from the CCD camera and the illumination system, and systematic errors from the CCD camera. The measurement component of the algorithm was developed using the process of edge detection, binarization and thining.</p>

<p>The paper concentrates on the practical engineering and technical aspects of the machine vision system for the purpose of assisting engineers in the development of advanced digital imaging systems. This is because other technological and scientific fields may benefit from these novel, practical techniques and the dissemination of details into the vision system.</p>

<p>In terms of forensic document analysis the advantage of this method compared with using optical instruments such as a travelling microscope for measuring small lengths is that it can deal relatively quickly with large sized samples with minimal handling. It is expected that future technical developments will combine this method with other digital imaging techniques that measure print area, texture and intensity to form a single integrated system. </p>

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