The development of an image analysis system that can detect fraudulent alterations made to printed images
Jack Tchan · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2004
An image analysis system that can differentiate between different black toners or inks non-destructively on printed text documents and images is currently under development at The London College of Printing. It is envisaged that the system will be able to find alterations in documents or images that are difficult to detect even by the most skilled expert document examiners using established forensic techniques. This paper describes the development of a nondestructive method that is intended to detect imperceptible fraudulent alterations to digital print samples. A digital image analysis system that incorporated a high-resolution low noise CCD monochrome camera with an optical system to enlarge images was used. Software that could obtain measurements of the relative optical reflectivity and sharpness characteristics of printed image areas from the raw image analysis data was developed. A single A4 sized paper sheet with a printed image that was produced using a combination of two different laser printers and an optical photocopier was illuminated using visible light. The results of subsequent image analysis measurements demonstrated it was possible to detect imperceptible alterations on the A4 sheet using this technique.