Photographic Reproduction
Definition
Lab-side imaging of a questioned document using controlled lighting (oblique, transmitted, coaxial), filters and wavelengths from UV through visible to IR, to reveal features the naked eye cannot see.
- Field
- Questioned document examination
- Lighting types
- Oblique, transmitted, coaxial
- Spectral range
- UV through visible to infrared
- Purpose
- Reveal features invisible to the naked eye
Common questions
Why would an examiner switch between oblique and transmitted lighting on the same document?+
Oblique lighting reveals surface texture such as indented writing or embossing, while transmitted light passing through the paper shows watermarks and internal features, so each lighting mode surfaces a different category of evidence.
What kinds of alterations does infrared photography commonly expose?+
Infrared imaging can reveal ink differences invisible in visible light, since some inks that look identical to the eye absorb or reflect infrared differently, exposing added or altered entries written with a different ink batch or pen.
Is photographic reproduction a destructive examination technique?+
No, it is non-destructive; it only involves capturing images under different light sources and wavelengths, which is one reason it is typically performed early, before any chemical or physical testing that could alter the document.
Related terms
- ESDA
- Electrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressure and writing...
- Inkjet Printing
- Non-impact printing that sprays liquid ink droplets onto paper. Two main technologies: thermal (HP, Canon, bubble-jet) and piezoelectric (Epson).
- IR Luminescence
- Emission of near-infrared radiation by ink dye molecules when excited by visible light; different ink formulations luminesce at different intensities, allowing differentiation...
- MIC / Yellow Tracking Dots
- Machine Identification Code: faint yellow micro-dots printed by many colour laser printers and copiers on every page, encoding serial number and timestamp....
- Oblique-Light Photography
- Photography of a document surface using illumination at a low angle (10 to 15 degrees from the paper plane), which casts shadows...
- Transmitted-Light Photography
- Light passed through the paper from behind to reveal watermarks, paper-fibre disturbance, security threads, erasures and chemical thinning.
- VSC-8000
- Video Spectral Comparator by Foster + Freeman, the standard QD instrument in CFSL and GEQD labs, with broadband visible, UV (254, 365...
- Xerography
- Dry electrophotographic process invented by Chester Carlson (1938). Photoconductive drum is charged, exposed to image, dusted with toner, transferred to paper and...