Doug Rogers

An Insight into Forensic Document Examiner Expertise for Discriminating Between Forged and Disguised Signatures

Abstract:  It has previously been shown that forensic document examiners (FDEs) have expertise in providing opinions about whether questioned signatures are genuine or simulated. This study extends the exploration of FDE expertise by evaluating the performance of eight FDEs and 12 control subjects at identifying signatures as either forgeries or the disguised writing of a specimen provider. Subject eye movements and response times were recorded with a Tobii 1750 eye tracker during the signature evaluations. Using a penalty scoring system, FDEs performed significantly better than control subjects (t = 2.465, p = 0.024), with one FDE able to correctly call 13 of the 16 test stimuli (and three inconclusive calls). An analysis of eye movement search patterns by the subjects indicated that a very similar search strategy was employed by both groups, suggesting that visual inspection of signatures is mediated by a bottom up search strategy. However, FDEs spent greater than 50% longer to make a decision than the control group. The findings are suggestive that for some stimuli FDEs can discriminate between forgeries and disguises, and that this ability is due to a careful inspection and consideration of multiple features within a signature.

The Dynamic Character of Disguise Behavior for Text-based, Mixed, and Stylized Signatures

Abstract:  The aims of this study were to determine if dynamic parameters (duration, size, velocity, jerk, and pen pressure) differed for signing style (text‐based, stylized, and mixed) and if signing style influences handwriting dynamics equally across three signature conditions (genuine, disguised, and auto‐simulation). Ninety writers provided 10 genuine signatures, five disguised signatures, and five auto‐simulated signatures. All 1800 signatures were collected using a digitizing tablet resulting in a database of each signature’s dynamic characteristics. With genuine signatures, there were significant differences between styles for size, velocity, and pen pressure, and there were significant differences between genuine signatures and at least one of the un‐natural signature conditions for all parameters. For velocity and size, these changes with condition were dependent on style. Changes with condition for the other parameters were similar for the three styles. This study shows that there are differences among natural signature styles and disguise behaviors that may be relevant in forensic signature examinations.

Forensic Document Examiners’ Skill in Distinguishing Between Natural and Disguised Handwriting Behaviors

Abstract:  Disguised handwriting is problematic for forensic document examiners (FDEs) and attracts higher misleading and inconclusive rates on authorship opinions than does genuine writing (Found B, Rogers D, International Graphonomics Society, 2005). There are currently no published empirical data on FDEs’ expertise in distinguishing between natural and disguised writing behavior. This paper reports on the skill of FDEs for determining the writing process of 140 pairs of natural and disguised writings and compares their results with those of a control group of laypeople. A significant difference was found between the examiner and lay group. FDEs’ expertise is characterized by their conservatism, where FDEs express a higher proportion of inconclusive opinions (23.1% for FDEs compared to 8.4% for the control group). This leads to the FDEs expressing a smaller percentage of misleading responses when calling writings as either naturally written or disguised (4.3% for FDEs compared with 12.2% for the control group).

Dynamic characteristics of signatures: effects of writer style on genuine and simulated signatures.

The aims of this study were to determine if computer‐measured dynamic features (duration, size, velocity, jerk, and pen pressure) differ between genuine and simulated signatures. Sixty subjects (3 equal groups of 3 signature styles) each provided 10 naturally written (genuine) signatures. Each of these subjects then provided 15 simulations of each of three model signatures. The genuine (N = 600) and simulated (N = 2700) signatures were collected using a digitizing tablet. MovAlyzeR® software was used to estimate kinematic parameters for each pen stroke. Stroke duration, velocity, and pen pressure were found to discriminate between genuine and simulated signatures regardless of the simulators own style of signature or the style of signature being simulated. However, there was a significant interaction between style and condition for size and jerk (a measure of smoothness). The results of this study, based on quantitative analysis and dynamic handwriting features, indicate that the style of the simulators own signature and the style of signature being simulated can impact the characteristics of handwriting movements for simulations. Writer style characteristics might therefore need to be taken into consideration as potentially significant when evaluating signature features with a view to forming opinions regarding authenticity.

A computer program designed to compare the spatial elements of handwriting

Abstract The comparison of questioned and standard line traces in forensic handwriting examination has to date been based almost entirely on subjective techniques. Handwriting examiners have not been equipped with a basic user-friendly technique to perform measurements on what are non-linear and variable behavioural artifacts. This paper describes a technique developed through research into human motor control which has been modified to be used by forensic handwriting examiners. The program provides a series of measurement tools. These tools can be applied to scanned images for the purpose of determining the spatial consistency of a disputed sample with a body of known writings. It is thought that the immediate application for this technique in the forensic casework environment is for the comparison of disputed signatures. In addition, the program can be used for any forensic research project requiring objective spatial data. If the field of forensic handwriting examination is to be considered a scientific endeavour, then the move toward the inclusion of objective measurement as part of the overall comparison methodology must be made.

Nonadherence to the isochrony principle in forged signatures

Highly programmed skilled movements are executed in such a way that their kinematic features adhere to certain rules referred to as minimization principles. One such principle is the isochrony principle, which states that the duration of voluntary movement remains approximately constant across a range of movement distances; that is, movement duration is independent of movement extent. The concept of isochrony suggests that some information stored in the motor program is constant, thus reducing the storage demands of the program. The aim of the present study was to examine whether forged signatures can be distinguished from genuine signatures on the basis of isochrony kinematics. Sixty writers were asked to write their own signatures and to forge model signatures representing three different writing styles: text-based, stylized, and mixed. All signatures were digitized to enable high precision dynamic analyses of stroke kinematics. Vertical stroke duration and absolute amplitude were measured for each pen stroke of the signatures using MovAlyzeR(®) software. Slope coefficients derived from simple regression models of the relationship between stroke duration and amplitude served as our measure of isochrony. The slope coefficient reflects the degree to which stroke duration increases in relation to stroke amplitude. Higher coefficients indicate greater increases in stroke duration for a given stroke amplitude and thus violate the isochrony principle. We hypothesized that the duration-amplitude coefficients for forged signatures would be significantly greater than for genuine signatures suggesting non-adherence to the isochrony principle. Results indicated that regardless of the style of the writer, genuine signatures were associated with low slope coefficients Pen strokes forming forged signatures had significantly greater duration-amplitude slope coefficients than genuine signatures. These findings suggest that when forging signatures, writers execute pen movements having steeper duration-amplitude relationships than for genuine signatures.

Eye Movement Evaluation of Signature Forgeries: Insights to Forensic Expert Evidence

Signatures are a complex and important biometric that have widespread international acceptance for verifying individual identity. As with other security measures, there are often attempts to mislead authorities by simulating genuine signatures. The ability to reliably identify genuine signatures from simulations is an area of forensic science of high value to legal proceedings, and several studies have established an expertise effect between forensic document examiners (FDEs) and control subjects. Eye movement recordings of the visual processing of FDEs during signature evaluations reveal that examiner expertise results from an enhanced capacity to process local features in the context of global information. In addition, eye movement studies allow for an understanding of how high- and low-complexity ranked signatures are visually inspected by subjects when making simulations. We discuss the importance of understanding the context of a work environment for designing experiments to reveal mechanisms of expertise used by professionals to do their job. We, thus, look at the normal work environment of FDEs for evaluating signatures and how the requirement of understanding expertise from a legal standpoint has facilitated considerable interest in eye-tracking technologies. In particular, we argue that the accurate modelling of the work environment is central to deriving parameters for use in eye movement studies to understand the role of expertise in subjects.