9 February 2006 Sub-pixel analysis to support graphic security after scanning at low resolution
Author Affiliations +
Abstract
Whether in the domain of audio, video or finance, our world tends to become increasingly digital. However, for diverse reasons, the transition from analog to digital is often much extended in time, and proceeds by long steps (and sometimes never completes). One such step is the conversion of information on analog media to digital information. We focus in this paper on the conversion (scanning) of printed documents to digital images. Analog media have the advantage over digital channels that they can harbor much imperceptible information that can be used for fraud detection and forensic purposes. But this secondary information usually fails to be retrieved during the conversion step. This is particularly relevant since the Check-21 act (Check Clearing for the 21st Century act) became effective in 2004 and allows images of checks to be handled by banks as usual paper checks. We use here this situation of check scanning as our primary benchmark for graphic security features after scanning. We will first present a quick review of the most common graphic security features currently found on checks, with their specific purpose, qualities and disadvantages, and we demonstrate their poor survivability after scanning in the average scanning conditions expected from the Check-21 Act. We will then present a novel method of measurement of distances between and rotations of line elements in a scanned image: Based on an appropriate print model, we refine direct measurements to an accuracy beyond the size of a scanning pixel, so we can then determine expected distances, periodicity, sharpness and print quality of known characters, symbols and other graphic elements in a document image. Finally we will apply our method to fraud detection of documents after gray-scale scanning at 300dpi resolution. We show in particular that alterations on legitimate checks or copies of checks can be successfully detected by measuring with sub-pixel accuracy the irregularities inherently introduced by the illegitimate process.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Bertrand Haas, Robert Cordery, Hongmei Gou, Steve Decker, "Sub-pixel analysis to support graphic security after scanning at low resolution", Proc. SPIE 6075, Optical Security and Counterfeit Deterrence Techniques VI, 60750B (9 February 2006); doi: 10.1117/12.641516; https://doi.org/10.1117/12.641516
PROCEEDINGS
13 PAGES


SHARE
RELATED CONTENT

Digital authentication with copy-detection patterns
Proceedings of SPIE (June 03 2004)
Banknotes and unattended cash transactions
Proceedings of SPIE (April 07 2000)
The new color of money: safer, smarter, more secure
Proceedings of SPIE (June 03 2004)
Creating variable data UV signals for security applications
Proceedings of SPIE (January 28 2008)
Design methodology of Dutch banknotes
Proceedings of SPIE (April 07 2000)

Back to Top