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Pattern matching finds CD forgers

11 Nov 2004

An Irish start-up unveils a machine vision system that traces optical discs back to the machine where they were pressed.

DiscMatch, a machine vision system that traces an optical disc back to the pressing machine in which it was created, could soon be causing counterfeiters some headaches. The system searches for marks inadvertently left on the disc from its manufacturing process and gives authorities vital evidence in their search for fraudulent activity.

The counterfeiting of compact discs represents a significant loss to copyright holders. The IFPI, a global body representing the recording industry, estimates that 1.1 billion pirate music discs were made in 2003 alone and that 35% of all CD music sold is pirate.

DiscMatch is the brainchild of a 3-year-old Irish company called FraudHalt. Knowing that security features deliberately introduced in media can be copied, the firm started looking for imprints left on the disc during manufacturing which are impossible to forge.

An optical disc is made from a mould comprising two plates. The first plate contains the pattern of pits which represents the data on the CD while the second is an optically-flat mirror.

To look for CDs that have been made from the same mould, DiscMatch images the disc's stacking ring, a 1.5 mm wide raised ring around the central hole in the CD. This ring is formed by a recess in the mirror plate and leaves a unique pattern of marks on its surface. These "signature" patterns can then be traced back to a mirror plate in a specific pressing machine.

DiscMatch images the entire stacking ring using a microscope with up to 5x magnification, darkfield illumination and a 2D translation stage. A CCD camera records images of the ring's surface. A complete scan takes 4.5 minutes to perform and contains 91 frames which are stitched together.

A matching algorithm then analyses the images and looks for a match with existing scans held in a library.

"Our aim is to build a library of fingerprints from both legitimate and counterfeit sources," said Patrick Smith, the FraudHalt's chief product architect. "Due to the limited number (around 1000) of compact disc production machines it is quite feasible to build a near-complete library - at least of legitimate sources."

This work was presented at SPIE's Optics and Photonics for Security and Defense Symposium held in London in October.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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