Validation of image stream hashing: A forensic method for content verification

How do forensic examiners know if they have altered an image stream when converting a digital image from one codec or file container to another for analysis? Forensic standards and best practices recommend avoiding alteration or degradation of multimedia data during transcoding. An image stream hashing method was recently introduced to the forensic science community to answer the question above. This paper offers an initial validation study of image stream hashing method that may answer the question above. The first half of the study's experiments tested the image stream hashing method to measure fitness for use in forensic science while identifying errors and limitations. The study's second phase analyzed the systematic errors detected in initial tests to discover error causation. Causation analysis identified four method limitations subsequently used to develop proposed standard controls of method operations. The final study phase repeated the initial experiments used in the first phase while implementing the proposed standard controls of method operations. Initial test results indicated the method had significant error rates, limiting the effectiveness of the method to only three of the five file types used in the study. The final testing phase revealed that implementing proposed standard controls of method operations reduced the potential systematic errors to a negligible level when using the image stream hashing method for content verification. The validation study concluded that examiners could use the image stream hashing method for forensic science only by implementing error mitigation techniques that utilize the proposed standard controls of method operations.     

The accuracy and validity of the Sheffield Features of Gait Tool

Gait is now widely used in the UK as a contributor to identification, and increasing interest is being shown in its use in both Europe and the US. One of the long standing criticisms of the use of gait as evidence has been the lack of a validated standard methodology. With the publication of the ‘Code of practice for forensic gait analysis’, and the adoption of the code as part of the ‘Codes of Practice and Conduct for forensic science providers and practitioners in the Criminal Justice System’ by the Forensic Science Regulator, forensic gait analysts are now required to provide evidence of the testing of the methods used. The Sheffield Features of Gait Tool is specifically designed to assist observational gait analysis in the forensic context, and was developed by forensic gait analysis practitioners based on their casework and trial experience. Birch et al 2019 reported the findings of a study undertaken to assess the repeatability and reproducibility of the tool. This paper reports the findings of a study undertaken to assess the accuracy with which analysts identified features of gait when using the tool.Fourteen participants, with experience in observational gait analysis, viewed footage of computer generated avatars walking, and completed the features of gait tool on multiple occasions. The results showed a mean accuracy score of 134.92 out of a possible 180 (74.96%), a standard deviation of 9.49 (5.27%) and a coefficient of variation of 7.03%, demonstrating a good degree of consistency between the scores (Cronbach’s alpha <0.90; ANOVA p-value <0.05).The findings of this study, coupled with those of the Birch et al 2019 study which showed there to be good levels of both repeatability and reproducibility of observations of features of gait made by the participants, suggest that the Sheffield Features of Gait Tool is a valid and fit for purpose method of observing and recording features of gait in the forensic context. The use of the tool provides the basis of a standardised methodology for observational gait analysis in the forensic context.     

What does method validation look like for forensic voice comparison by a human expert?

Method validation has gained traction within forensic speech science. The community recognises the need to demonstrate that the analysis methods used are valid, but finding a way to do so has been more straightforward for some analysis methods than for others. This article addresses the issue of method validation for the Auditory Phonetic and Acoustic (AuPhA) approach to forensic voice comparison. Although it is possible to take inspiration from general regulatory guidance on method validation, it is clear that these cannot be transposed on to all forensic analysis methods with the same degree of success. Particularly with respect to an analysis method like AuPhA, and in a field of the size and characteristics of forensic speech science, a bespoke approach to method validation is required. In this article we address the discussions that have been taking place around method validation, and illustrate one possible solution to demonstrating the validity of voice comparison by a human expert using the AuPhA method. In doing so we consider the constraints placed on sole practitioners, which generally go unacknowledged.     

Relative effects of posture and activity on human height estimation from surveillance footage

Height estimations based on security camera footage are often requested by law enforcement authorities. While valid and reliable techniques have been established to determine vertical distances from video frames, there is a discrepancy between a person's true static height and their height as measured when assuming different postures or when in motion (e.g., walking). The aim of the research presented in this report was to accurately record the height of subjects as they performed a variety of activities typically observed in security camera footage and compare results to height recorded using a standard height measuring device. Forty-six able bodied adults participated in this study and were recorded using a 3D motion analysis system while performing eight different tasks. Height measurements captured using the 3D motion analysis system were compared to static height measurements in order to determine relative differences. It is anticipated that results presented in this report can be used by forensic image analysis experts as a basis for correcting height estimations of people captured on surveillance footage.     

司法鉴定领域分类和能力范围表述的国内外比较研究

对司法鉴定领域开展科学、有效的分类,进行统一规范的能力范围表述,有助于建立完整的司法鉴定标准化体系,能为司法鉴定机构合理规划组织结构、准确定位发展方向提供指引,也能为司法鉴定行业管理部门的规范化管理提供帮助。对该领域分类和能力表述开展国内外比较分析,是实现上述目标的基础性研究。目前我国在司法鉴定领域的分类方法尚未统一,与国外法庭科学认可分类方法相比,尚有部分项目未纳入分类范围之内;国内能力范围表述在目的、方式、详细程度上与国外相比亦有不同。本文对国内外行业管理组织和国际权威认可机构司法鉴定领域分类及能力范围表述进行了比较分析,研究解析其内容及差异,并提出了制定司法鉴定领域分类国家标准、扩展司法鉴定领域分类内容、适时调整司法鉴定能力范围表述内容等建议。     

The effect of frame rate on the ability of experienced gait analysts to identify characteristics of gait from closed circuit television footage

Forensic gait analysis is increasingly being used as part of criminal investigations. A major issue is the quality of the closed circuit television (CCTV) footage used, particularly the frame rate which can vary from 25 frames per second to one frame every 4 s. To date, no study has investigated the effect of frame rate on forensic gait analysis. A single subject was fitted with an ankle foot orthosis and recorded walking at 25 frames per second. 3D motion data were also collected, providing an absolute assessment of the gait characteristics. The CCTV footage was then edited to produce a set of eight additional pieces of footage, at various frame rates. Practitioners with knowledge of forensic gait analysis were recruited and instructed to record their observations regarding the characteristics of the subject's gait from the footage. They were sequentially sent web links to the nine pieces of footage, lowest frame rate first, and a simple observation recording form, over a period of 8 months. A sample-based Pearson product-moment correlation analysis of the results demonstrated a significant positive relationship between frame rate and scores (r = 0.868, p = 0.002). The results of this study show that frame rate affects the ability of experienced practitioners to identify characteristics of gait captured on CCTV footage. Every effort should therefore be made to ensure that CCTV footage likely to be used in criminal proceedings is captured at as high a frame rate as possible.     

IoT forensics: Exploiting unexplored log records from the HIKVISION file system

CCTV surveillance systems are IoT products that can be found almost everywhere. Their digital forensic analysis often plays a key role in solving crimes. However, it is common for these devices to use proprietary file systems, which frequently hinders a complete examination. HIKVISION is a well-known manufacturer of such devices that typically ships its products with its proprietary file system. The HIKVISION file system has been analyzed before but that research has focused on the recovery of video footage. In this paper, the HIKVISION file system is being revisited regarding the log records it stores. More specifically, these log records are thoroughly examined to uncover both their structure and meaning. These unexplored pieces of evidence remain unexploited by major commercial forensic software, yet they can contain critical information for an investigation. To further assist digital forensic examiners with their analysis, a Python utility, namely the Hikvision Log Analyzer, was developed as part of this study that can automate part of the process.     

Shifting forensic science focus from means to purpose: A path forward for the discipline?

Forensic science is facing a persistent crisis that is often addressed by organizational responses, with a strong focus on the improvement and standardisation of means and processes. However, organisations and processes are highly dependent on the political, economical and legal structures in which they operate. This may explain why most proposed solutions had difficulties in addressing the crisis up to now, as they could hardly be applied transversally to all forensic science models. Moreover, new tools and technologies are continuously developed by a quasi-infinite number of different scientific disciplines, thus leading to further diversity and fragmentation of forensic science. In this paper, it is proposed to shift the focus from means to purpose and consider forensic science current challenges in terms of discipline, before addressing organisations’ specific issues. As a distinct discipline, forensic science can refocus research and development on shared principles and purposes, such as reconstructing, monitoring, and preventing crime and security issues. This focus change will facilitate a better understanding of the trace as the object of study of forensic science and eventually lead to a more impactful and long-lasting effect. This approach will also foster the development of a forensic science culture (instead of a primarily technological culture) unified by purpose rather than means through more relevant education and research.     

Public beliefs about the accuracy and importance of forensic evidence in the United States

Recent advances in forensic science, especially the use of DNA technology, have revealed that faulty forensic analyses may have contributed to miscarriages of justice. In this study we build on recent research on the general public’s perceptions of the accuracy of 10 forensic science techniques and of each stage in the investigation process. We find that individuals in the United States hold a pessimistic view of the forensic science investigation process, believing that an error can occur about half of the time at each stage of the process. We find that respondents believe that forensics are far from perfect, with accuracy rates ranging from a low of 55% for voice analysis to a high of 83% for DNA analysis, with most techniques being considered between 65% and 75% accurate. Nevertheless, respondents still believe that forensic evidence is a key part of a criminal case, with nearly 30% of respondents believing that the absence of forensic evidence is sufficient for a prosecutor to drop the case and nearly 40% believing that the presence of forensic evidence – even if other forms of evidence suggest that the defendant is not guilty – is enough to convict the defendant.     

Digital behavioral-fingerprint for user attribution in digital forensics: Are we there yet?

the need for a reliable and complementary identifier mechanism in a digital forensic analysis is the focus of this study. Mouse dynamics have been applied in information security studies, particularly, continuous authentication and authorization. However, the method applied in security is void of specific behavioral signature of a user, which inhibits its applicability in digital forensic science. This study investigated the likelihood of the observation of a unique signature from mouse dynamics of a computer user. An initial mouse path model was developed using non-finite automata. Thereafter, a set-theory based adaptive two-stage hash function and a multi-stage rule-based semantic algorithm were developed to observe the feasibility of a unique signature for forensic usage. An experimental process which comprises three existing mouse dynamics datasets were used to evaluate the applicability of the developed mechanism. The result showed a low likelihood of extracting unique behavioral signature which can be used in a user attribution process. Whilst digital forensic readiness mechanism could be a potential approach that can be used to achieve a reliable behavioral biometrics modality, the lack of unique signature presents a limitation. In addition, the result supports the logic that the current state of behavioral biometric modality, particularly mouse dynamics, is not suitable for forensic usage. Hence, the study concluded that whilst mouse dynamics-based behavioral biometrics may be a complementary modality in security studies, more will be required to adopt it as a forensic modality in litigation. Furthermore, the result from this study finds relevance in other human attributional studies such as user identification in recommender systems, e-commerce, and online profiling systems, where the degree of accuracy is not relatively high.     

Identifying and measuring juror pre-trial bias for forensic evidence: development and validation of the Forensic Evidence Evaluation Bias Scale

Abstract

Previous research has provided support for the impact of juror pre-trial bias on judicial decision making, particularly in cases where the evidence presented at trial is of weak or ambiguous probative value. In an effort to identify whether a pre-trial bias for forensic evidence exists, the Forensic Evidence Evaluation Bias Scale (FEEBS) was developed and tested. The results of a principal components analysis suggested that two distinct constructs were being measured, corresponding to a pro-prosecution and pro-defence bias toward forensic evidence. In a second validation study, scores on these two subscales were compared with other existing juror bias measures (Juror Bias Scale and Belief in a Just World) and in a mock juror decision making task only the pro-prosecution subscale of the FEEBS predicted the perceived strength of forensic evidence. A partial mediation model is presented which explains the relationship between this bias and verdict preferences. The implications of this potential juror bias are discussed in the context of real juries, the CSI Effect (which refers to anecdotal claims that jurors are biased by the popularity of fictional representations of forensic science on television) and peremptory challenges, as well as future research directions.     

Error and its Meaning in Forensic Science

The discussion of “error” has gained momentum in forensic science in the wake of the Daubert guidelines and has intensified with the National Academy of Sciences' Report. Error has many different meanings, and too often, forensic practitioners themselves as well as the courts misunderstand scientific error and statistical error rates, often confusing them with practitioner error (or mistakes). Here, we present an overview of these concepts as they pertain to forensic science applications, discussing the difference between practitioner error (including mistakes), instrument error, statistical error, and method error. We urge forensic practitioners to ensure that potential sources of error and method limitations are understood and clearly communicated and advocate that the legal community be informed regarding the differences between interobserver errors, uncertainty, variation, and mistakes.     

The Effect of Image Quality and Forensic Expertise in Facial Image Comparisons

Images of perpetrators in surveillance video footage are often used as evidence in court. In this study, identification accuracy was compared for forensic experts and untrained persons in facial image comparisons as well as the impact of image quality. Participants viewed thirty image pairs and were asked to rate the level of support garnered from their observations for concluding whether or not the two images showed the same person. Forensic experts reached their conclusions with significantly fewer errors than did untrained participants. They were also better than novices at determining when two high‐quality images depicted the same person. Notably, lower image quality led to more careful conclusions by experts, but not for untrained participants. In summary, the untrained participants had more false negatives and false positives than experts, which in the latter case could lead to a higher risk of an innocent person being convicted for an untrained witness.     

Educating Jurors about Forensic Evidence: Using an Expert Witness and Judicial Instructions to Mitigate the Impact of Invalid Forensic Science Testimony

Invalid expert witness testimony that overstated the precision and accuracy of forensic science procedures has been highlighted as a common factor in many wrongful conviction cases. This study assessed the ability of an opposing expert witness and judicial instructions to mitigate the impact of invalid forensic science testimony. Participants (N = 155) acted as mock jurors in a sexual assault trial that contained both invalid forensic testimony regarding hair comparison evidence, and countering testimony from either a defense expert witness or judicial instructions. Results showed that the defense expert witness was successful in educating jurors regarding limitations in the initial expert's conclusions, leading to a greater number of not-guilty verdicts. The judicial instructions were shown to have no impact on verdict decisions. These findings suggest that providing opposing expert witnesses may be an effective safeguard against invalid forensic testimony in criminal trials.     

Research Progress on Postmortem Interval Estimation by Vitreous HumorCSCD

Postmortem interval (PMI)estimation is one of the most challenging problems in the field of forensic science. Vitreous humor is a hotspot which has been used for PMI estimation and postmortem chemical analysis in forensic pathology. In order to provide novel perspectives for the future research of PMI estimation using vitreous humor, the comparison between vitreous humor with other common body fluids, the effect of temperature on vitreous humor, vitreous humor detection method and data fitting method have been reviewed in this paper. © 2018 by the Editorial Department of Journal of Forensic Medicine.     

Computed dental radiography used to reproduce antemortem film position

Visual comparison of conventional antemortem and postmortem dental radiographs is often included in forensic identification. Ten forensic cases employing dry mandibular and maxillary bones and a dry study skull were exposed using the CDR digital dental X-ray system developed by Schick Technologies, Inc. Exposures of 0.08s at 10 mA and 70 kVp were taken with an INTREX intraoral dental X-ray unit. Digital radiography has the ability to produce an image instantaneously, allowing an operator to retake an incorrectly aligned radiograph almost immediately. It gives the forensic scientist a simplified method for reproducing antemortem radiographic position more efficiently and often with greater accuracy than conventional radiography.     

Community Members’ Perceptions of the CSI Effect

The CSI Effect is the notion that crime show viewing influences jurors to have unrealistic expectations of forensic evidence, which then affects their trial decisions. Analyses of popular media shows that the media portrays the effect as a real problem, and research surveying the legal community indicates that they believe the CSI Effect exists and may change their investigation and trial strategies accordingly. The present study expanded on this research by surveying community members regarding their perceptions of the CSI Effect. Community members reported their general television and crime show viewing behaviors, and we examined this in relation to their knowledge construction of the CSI Effect. Findings indicate that overall, the majority of community members did not have knowledge of the CSI effect, but those who did perceive it as an unrealistic expectation of evidence. When provided with a definition of the CSI Effect, people generally believed it exists. Additionally, crime show viewing and participant’s race influenced people’s perceptions of the CSI effect. Limitations of this study and directions for future research are also discussed.     

代谢物组学及法医学新机遇——创建代谢物组学数据库及专家系统的设想

法医学DNA技术促成了法医学实践的一次飞跃,其建立的数据库策略为后续的研究提供了可贵的借鉴;2004年召开的人类基因组大会提出并肯定了代谢物组学的理论和技术,该技术相对于目前应用的其它技术并结合法医学的实践需要,具有更广阔的应用前景,本文借鉴DNA技术成功的经验,首次提议建立代谢物组学数据库及基于该数据库的专家系统,为解决目前法医学难以解决的难题,促成法医学继DNA技术之后新飞跃进行探索.