刑事数码摄影中应注意的问题

随着数字技术的发展，数码摄影应用于刑事摄影领域也是历史发展的必然。因为数码相机与传统相机存在本质区别，根据实际办案的需要．选择适当数码相机和数字图像存储格式，根据数码相机的原理及其特点，重新认识数码相机的参数，使数码相机在刑事技术中充分发挥其应有的作用。     

数码相机在拍摄犯罪现场中的应用

与传统的胶片相机相比较,数码相机有许多优点.在刑事摄影中,数码相机已越来越多地应用于犯罪现场照相.要获取符合要求的数码现场照片,应把握数码相机的基本类型、结构、特点,熟练掌握其拍摄方法和技巧.     

Simulation-based reconstruction of traffic incidents from moving vehicle mono-camera

Video recordings from digital cameras implemented in road vehicles present a valuable source of data concerning various dangerous traffic situations, i.e., road accidents or near-miss incidents. This data is readily available and numerous methods for forensic reconstruction of traffic situations from vehicle video were presented in the past. New alternative method for reconstruction of traffic situations from vehicle video is presented in this article. The method is based on the fusion of kinetic vehicle trajectory simulation within 3D laser scanner point cloud, projective geometry, and processing of video footage from moving vehicle camera. The method offers accurate reconstruction of general vehicle motion within relevant time domain whereby in-depth technical information about traffic incident can be quantitatively extracted from video footage. The result is physics-based 3D projection of simulated vehicle motion on the motion of real vehicle recorded by moving monocular camera. The method was validated within performed experimental test runs with respect to vehicle speed, distance travelled, acceleration/deceleration and directional quantities (yaw rate, yaw angle). The method was further applied in the reconstruction of real-world traffic events.     

Forensic analysis of bicomponent fibers using infrared chemical imaging

The application of infrared chemical imaging to the analysis of bicomponent fibers was evaluated. Eleven nominally bicomponent fibers were examined either side-on or in cross-section. In six of the 11 samples, infrared chemical imaging was able to spatially resolve two spectroscopically distinct regions when the fibers were examined side-on. As well as yielding characteristic infrared spectra of each component, the technique also provided images that clearly illustrated the side-by-side configuration of these components in the fiber. In one case it was possible to prepare and image a cross-section of the fiber, but in general the preparation of fiber cross-sections proved very difficult. In five of the 11 samples, the infrared spectra could be used to identify the overall chemical composition of the fibers, according to a published classification scheme, but the fiber components could not be spatially resolved. Difficulties that are inherent to conventional "single-point" infrared spectroscopy, such as interference fringing and sloping baselines, particularly when analyzing acrylic type fibers, were also encountered in the infrared chemical image analysis of bicomponent fibers. A number of infrared sampling techniques were investigated to overcome these problems, and recommendations for the best sampling technique are given. Chemical imaging results were compared with those obtained using conventional fiber microscopy techniques.     

Using anisotropic diffusion for efficient extraction of sensor noise in camera identification

Each digital camera has an intrinsic fingerprint that is unique to each camera. This device fingerprint can be extracted from an image and can be compared with a reference device fingerprint to determine the device origin. The complexity of the filters proposed to accomplish this is increasing. In this note, we use a relatively simple algorithm to extract the sensor noise from images. It has the advantages of being easy to implement and parallelize, and working faster than the wavelet filter that is common for this application. In addition, we compare the performance with a simple median filter and assess whether a previously proposed fingerprint enhancement technique improves results. Experiments are performed on approximately 7500 images originating from 69 cameras, and the results are compared with this often used wavelet filter. Despite the simplicity of the proposed method, the performance exceeds the common wavelet filter and reduces the time needed for the extraction.     

Kurbanjan Samat: The Photographer

正KURBANJAN Samat couldn’t sleep on the night of March 1,2014,after hearing news that 29 people had been killed by eight Uygur assailants at Kunming Railway Station in Yunnan Province.Authorities identified the assailants as part of separatist forces from Xinjiang     

Forensic integrity verification of video recordings based on MTS files

Digital video is used in criminal trials as evidence with legal responsibility because video content vividly depicts events occurring at a crime scene. However, using sophisticated video editing software, assailants can easily manipulate visible clues for their own benefit. Therefore, the integrity of digital video files acquired or submitted as evidence must be ensured. Forensic analysis of digital video is key to ensuring the integrity of links with individual cameras. In this study, we analyzed whether it is possible to ensure the integrity of MTS video files. Herein, we propose a method to verify the integrity of MTS files encoded by advanced video coding high definition (AVCHD), which is frequently used for video recording. To verify MTS file integrity, we propose five features. Codec information, picture timing, and camera manufacture/model are modified AVI and MP4-like format video verification features. Group of pictures and Universally Unique Identifier patterns were specifically developed for MTS streams. We analyzed the features of 44 standard files recorded using all recording options of seven cameras. We checked whether integrity can be validated on unmanipulated videos recorded in various environments. In addition, we considered whether manipulated MTS files edited in video editing software could be validated. Experimental results show that all unmanipulated and manipulated MTS files with known recording devices were discriminated only when all five features were checked. These results show that the proposed method verifies the integrity of MTS files, strengthening the validity of MTS file-based evidence in trials.     

Identification of Mobile Phone and Analysis of Original Version of Videos through a Delay Time Analysis of Sound Signals from Mobile Phone Videos

This study designs a method of identifying the camera model used to take videos that are distributed through mobile phones and determines the original version of the mobile phone video for use as legal evidence. For this analysis, an experiment was conducted to find the unique characteristics of each mobile phone. The videos recorded by mobile phones were analyzed to establish the delay time of sound signals, and the differences between the delay times of sound signals for different mobile phones were traced by classifying their characteristics. Furthermore, the sound input signals for mobile phone videos used as legal evidence were analyzed to ascertain whether they have the unique characteristics of the original version. The objective of this study was to find a method for validating the use of mobile phone videos as legal evidence using mobile phones through differences in the delay times of sound input signals.     

BODY‐WORN CAMERAS AS A POTENTIAL SOURCE OF DEPOLICING: TESTING FOR CAMERA‐INDUCED PASSIVITY

Contentious debate is currently taking place regarding the extent to which public scrutiny of the police post‐Ferguson has led to depolicing or to a decrease in proactive police work. Advocates of the “Ferguson effect” claim the decline in proactive policing increased violent crime and assaults on the police. Although police body‐worn cameras (BWCs) are touted as a police reform that can generate numerous benefits, they also represent a form of internal and public surveillance on the police. The surveillance aspect of BWCs suggests that BWCs may generate depolicing through camera‐induced passivity. We test this question with data from a randomized controlled trial of BWCs in Spokane (WA) by assessing the impact of BWCs on four measures: officer‐initiated calls, arrests, response time, and time on scene. We employ hierarchical linear and cross‐classified models to test for between‐ and within‐group differences in outcomes before and after the randomized BWC rollout. Our results demonstrate no evidence of statistically significant camera‐induced passivity across any of the four outcomes. In fact, self‐initiated calls increased for officers assigned to treatment during the RCT. We discuss the theoretical and policy implications of the findings for the ongoing dialogue in policing.