Patents
US Patent 6,100,967
Monitoring of covert marks
Richard Farrar and Barry Hood
A method and apparatus for monitoring a body having a reflective surface, a coating layer of material transparent to visible light present on the surface and producing a covert optical discontinuity in an imagewise distribution on the layer, the imagewise distribution is such that it is visible via polarised light and viewing through a polarised filter.
[PDF : Covert marking patent 261 kB]
