Abstract: A method and apparatus for verifying the authenticity of bank notes or other notes having a security thread embedded therein, said apparatus comprising a scanning unit comprising at least one light source disposed opposite to at least one detector, wherein said at least one detector outputs a signal responsive to the transmitted light. As the bank note is swiped between the light source and detector the resultant output is processed, digitally encoded and correlated with stored characteristics corresponding to the transmission properties of an authentic bank note. These stored characteristics corresponding to the transmission properties of an authentic bank note are obtained by calibrating the apparatus with an authentic bank note.