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.     

根据数字全颌曲面断层片进行个体识别研究

目的建立中国恒乳牙交替完全人群数字全颌曲面断层片的同一认定方法。方法对120例中国恒乳牙交替完全人群的数字全颌曲面断层片进行测量和分析,对每颗牙齿的影像分别选取5个长度性指标和5个角度性指标,运用efilm workstation 2.1软件进行测量,SPSS 13.0软件对数据进行处理和统计。结果各观测指标的测量值在分段赋值区段里的分布概率有所不同,最大可达99.166 7%。两张同源数字全颌曲面断层片之间的分段赋值匹配概率最高为98.947 368 42%,最低为89.473 684 21%。结论所建立分段赋值匹配概率同一认定法经盲测验证,效果较好,该方法可为个体识别提供参考。     

物证鉴定的能力验证

能力验证是物证鉴定质量保障体系的重要组成部分,可以非常有效的评估、监控和提高实验室物证鉴定能力和质量。本文论述了物证鉴定能力验证的主要方法、形式、类型和特点,以及在物证鉴定实验室质量管理中的具体应用,介绍了国外物证鉴定实验室参加能力验证活动的历史和现状,并提出在我国物证鉴定实验室广泛开展能力验证活动的思考。     

Capturing high-resolution digital images for use in forensic document examination

In the past, pattern disciplines within forensic science have periodically faced criticism due to their subjective and qualitative nature and the perceived absence of research evaluating and supporting the foundations of their practices. Recently, however, forensic scientists and researchers in the field of pattern evidence analysis have developed and published approaches that are more quantitative, objective, and data driven. This effort includes automation, algorithms, and measurement sciences, with the end goal of enabling conclusions to be informed by quantitative models. Before employing these tools, forensic evidence must be digitized in a way that adequately balances high-quality detail and content capture with minimal background noise imparted by the selected technique. While the current work describes the process of optimizing a method to digitize physical documentary evidence for use in semi-automated trash mark examinations, it could be applied to assist other disciplines where the digitization of physical items of evidence is prevalent. For trash mark examinations specifically, it was found that high-resolution photography provided optimal digital versions of evidentiary items when compared to high-resolution scanning.     

Quantitative evaluation of the results of digital forensic investigations: a review of progress

Unlike conventional forensics, digital forensics does not at present generally quantify the results of its investigations. It is suggested that digital forensics should aim to catch up with other forensic disciplines by using Bayesian and other numerical methodologies to quantify its investigations’ results. Assessing the plausibility of alternative hypotheses (or propositions, or claims) which explain how recovered digital evidence came to exist on a device could assist both the prosecution and the defence sides in criminal proceedings: helping the prosecution to decide whether to proceed to trial and helping defence lawyers to advise a defendant how to plead. This paper reviews some numerical approaches to the goal of quantifying the relative weights of individual items of digital evidence and the plausibility of hypotheses based on that evidence. The potential advantages enabling the construction of cost-effective digital forensic triage schemas are also outlined.

Key points

• The absence of quantified results from digital forensic investigations, unlike those of conventional forensics, is highlighted.
• A number of approaches towards quantitative evaluation of the results of digital forensic investigations are reviewed.
• The significant potential benefits accruing from such approaches are discussed.

     

法庭科学毒物分析实验室质量控制的发展与现状

本文综述了国内外法庭科学毒物分析实验室质量控制的发展及一般要求,并讨论了我国毒物分析实验室质量控制中存在的不足和应对措施。     

Pre-set estimation-based in-silico silhouette-based methodology for improving the robustness to viewing direction difference for assisting forensic gait analysis

Forensic gait analysis is used to visually and quantitatively analyze information regarding the appearance and style of walking that can be presented as evidence in the court. The demand for analyzing CCTV pedestrian footage in video surveillance has been increasing. The dependence of the accuracy of semiautomatic silhouette-based analysis, often used in forensic science, on the differences in the viewing directions is a very challenging issue that is yet to be resolved for real case applications. Currently, the different viewing directions used in comparison footage significantly decrease the accuracy of same person analysis when using the silhouette-based method, often used in the Japanese forensic science domain. A calibration-based method was previously prosed to resolve this problem, but it requires performing an elaborate measurement procedure at the camera installation site for an accurate analysis. In this study, we propose a novel in-silico silhouette-based analysis method that significantly expands the number of viewing direction pre-set settings to 900 from the 24 used in the previous method. Several software tools have been developed to ensure that all the procedures can be executed on a computer. The experimental results confirm that the accuracy of the proposed method is comparable to that of the calibration-based method. Furthermore, the practical comparison results from actual consultation confirmed the effectiveness of the proposed method under existing viewing direction differences. We therefore anticipate that the proposed method will be beneficial for improving the analysis accuracy in real cases and therefore serve as a substitute of the previous method.