Advanced questioned document imaging technique can reveal the order in which ink layers are added to handwritten and printed documents

foster+freeman authored publication details the use of VSC Photometric Stereo and Elastomeric Sensor Imaging to interrogate and analyse questioned documents to understand the sequence of activity level features – ink line intersections, toner/ink boundaries etc.

Authored by researchers at foster+freeman, and published by the esteemed Science and Justice Journal, ‘Evaluation of Photometric Stereo and Elastomeric Sensor Imaging for non-destructive 3D analysis of Questioned Documents – A Pilot Study’, is a new and significant piece of work that demonstrates how a little used 3D imaging technique is capable of measuring the 3D morphology of a document in order to ascertain the sequence in which inks (pen strokes, toner etc.) are applied to a document.

Fig 1: Toner first /pen mark second

Photometric Stereo 3D imaging (PS)

An advanced forensic imaging tool available to users of the foster+freeman VSC8000/HS QDE workstation, PS 3D imaging is a powerful technique that can enhance the examination and authentication of various types of documents including handwritten notes, signatures, and printed materials. The method utilises multiple light sources, including near-IR (NIR) imaging, to capture detailed surface information for the creation of a three-dimensional representation of the document. This 3D representation may enhance the visibility of surface details, highlight subtle differences and variations in surface properties, and reveal indentations, ink layers, alterations, or erasures that may not be readily visible under normal lighting conditions or with conventional imaging techniques.

Elastomeric Sensor Imaging (ESI)

Elastomeric sensor imaging is an emerging technology that holds great potential for forensic document analysis providing valuable insights into indentations, pressure distribution, ink characteristics, document aging, and surface properties. Importantly, the technique offers a level of scientific robustness and quantification that is not present in the PS technique.

Fig 2: Red arrows indicate the toner/pen mark intersection.

Fig 3: Region of a document imaged using the VSC8000/HS Photometric Stereo option

Document Alteration Detection and Surface Detail Enhancement

Used individually or in combination, both PS and ESI provide examiners with an effective tool for detecting alterations, additions, or erasures on documents. By examining the PS 3D model of the document or by analysing the ESI derived topographical information, forensic experts can identify discrepancies, such as variations in surface elevation or disruptions in the natural flow of the document’s texture, which may indicate the sequence in which inks were applied to a document and possibly reveal attempts at tampering or fraudulent modifications.

Publication Details:

Justin Gould, Simon Clement, Bradley Crouch, Roberto S.P. King,

Evaluation of photometric stereo and elastomeric sensor imaging for the non-destructive 3D analysis of questioned documents – A pilot study,

Science & Justice, Volume 63, Issue 4, 2023, Pages 456-467,
ISSN 1355-0306

https://doi.org/10.1016/j.scijus.2023.04.016
(https://www.sciencedirect.com/science/article/pii/S1355030623000497)

Abstract:

Photometric Stereo and Elastomeric Sensor Imaging were assessed for measuring the 3-dimensional (3D) morphology of questioned document samples. Photometric stereo is shown to be a powerful non-contact technique for revealing micron level detail of the samples examined. Elastomeric Sensor Imaging is shown to complement photometric stereo by yielding equivalent results. Additionally, this technique allows quantification of the morphological depth information. The techniques were applied to 2 different types of questioned document sample. Firstly, written signatures were examined. Both techniques were able to reveal characteristic features that could be used to infer stroke direction and ink line application sequence. Secondly toner/ink intersections were examined. Both techniques allowed visualisation of 3D features which were used to infer the sequence of application.