Tartan Threads : a method for the real-time digital recognition of secure documents in ink-jet printers

Abstract

Thanks to today's digital imaging technology, any ten year old child with basic computer skills can create convincing counterfeit currency. It comes as no surprise that as output quality and costs have improved in ink-jet printers, there has been a corresponding surge in digital counterfeiting of security documents. The design of a system, through which a printer can recognize a security or other protected document though identification of a watermark, presents a challenge for the application of information hiding techniques. The marking should be strong enough to provide certainty that a document was intentionally marked and robust enough to withstand the transformations inherent in the scanning and printing process. Using an extended spread­spectrum technique, a small one-dimensional thread encoded with a known multi-bit signature is generated. If the printer detects a match, printing halts and a warning message is output to the user. By applying several such threads at varying orientations, this can provide an effective first line of defense against the casual digital counterfeiter.