We describe an optical forensic method for tracing a CD back to the pressing machine in which it was created, and present a system we have developed which maintains a library of the 'fingerprints' of such machines and can compare sample CDs against this library. In principle, any security feature that is deliberately created can be copied by a counterfeiter. In our forensic method we concentrate on features that arise spontaneously in the manufacturing process. Such features act as a signature or 'fingerprint'. In the case of CDs we show how the moulding process leaves an imprint of an unpolished part of the 'mirror plate' on the CD surface. Using machine vision and pattern-matching, we demonstrate the use of the system to acquire a positive match of a sample against a pre-recorded library entry created using a different CD from the same mould.
We present recent commercial anti-counterfeit projects that use machine-vision principles, to either verify genuine documents or trace the origin of counterfeits. In the first case we show how the characteristic nature of a reflection hologram, as used on a credit card, can be used to verify it quickly and economically. Many counterfeit holograms can be discriminated from a genuine example by a two-step test: first, that the visible object displayed by the hologram has the correct form when viewed at a given angle, and second, that the object changes in the correct way as the viewing angle is varied. Both of these can be implemented using a machine-vision system as we describe. Another application of machine-vision techniques in an anti-counterfeit context is their use in forensic investigation. We demonstrate how the origin of compact disks can be traced using marks in the outer surface, by imaging a magnified portion of the CD surface under darkfield illumination to maximise outer surface features while suppressing reflections from the internal data surface. We show that CDs from the same pressing machine exhibit matching defect patterns under darkfield illumination. This technique can be used to trace the origin of a sample counterfeit CD.