Authentication apparatus for moving value documents

An apparatus that authenticates a value document moving at a uniform velocity and which comprises a pre-selected covert composition that absorbs exciting incident light and emits optical radiation having a pre-selected emission wavelength, the apparatus comprising:

• an exciting light source that produces illumination of sufficient intensity to excite the pre-selected covert composition within an area illuminated by the exciting light source;
• optionally an optical filter that filters the pre-selected emission wavelength emitted from the pre-selected covert composition within the illuminated area;
• a first detector element and a second detector element housed in at least one photodetector, wherein the first detector element receives a first image of an area of the value document at a first time and outputs electronic signal data for the first image, and the second detector element receives a second image of substantially the same area of the value document at a second time and outputs electronic signal data for the second image, the first and second images corresponding to decay time intensity of the pre-selected emission wavelength emitted from the pre-selected covert composition;
• and
• a processing unit that collects and evaluates the output electronic signal data, and determines pass or failure data for the value document.