The detection and enhancement of latent fingermarks using infrared chemical imaging

The use of a new technique, Fourier transform infrared (FTIR) chemical imaging, has been demonstrated for the enhancement of latent fingermarks on a number of surfaces. Images of untreated fingermarks on glass backgrounds with excellent ridge detail were acquired using infrared chemical imaging. High quality fingermarks on glass backgrounds were also developed using ethyl cyanoacrylate (super glue) fuming and subsequent infrared chemical imaging. This new method allows the collection of images from backgrounds that traditionally pose problems for current fingermark detection methods. The background may, for example, be highly colored, have a complex pattern, or possess other pattern or image characteristics that make it difficult to separate fingermark ridges using traditional optical or luminescent visualization. One background that has proven to be a challenging surface for the development of latent fingermarks is the Australian polymer banknote. To demonstrate the power and applicability of infrared chemical imaging, fingermarks fumed with ethyl cyanoacrylate were successfully imaged from Australian polymer banknotes.     

Four novel alkyl 2-cyanoacylate monomers and their use in latent fingermark detection by mid-infrared spectral imaging

Four novel alkyl 2-cyanoacrylate monomers (alkyl=1-cyanoethyl, 2-cyanoethyl, trideuteromethyl and pentadeuteroethyl) have been tested for their ability to develop latent fingermarks that can then be visualized using mid-infrared spectral (chemical) imaging. Each of the four monomers was chosen for its potential to produce a strong, isolated infrared spectral band in its corresponding polymer (to provide spectral contrast against most backgrounds), as well as for its potential ability to be fumed onto fingermarks in the manner of conventional ethyl 2-cyanoacrylate (superglue). With the exception of the 2-cyanoethyl 2-cyanoacrylate, which had to be fumed under reduced pressure, all of the monomers were found to be sufficiently volatile to be fumed in a conventional fuming cabinet. All four monomers polymerized selectively on fingermark ridges on a variety of non-porous and semi-porous surfaces, leading to excellent development of the fingermarks. Unfortunately, although high quality mid-infrared spectral images of the fingermarks could be formed for all of the polymers at various frequencies, the new CN or CD stretching vibrations did not give rise to strong enough absorption intensities for good contrast on difficult backgrounds such as polymer banknotes. However, in the 1-cyanoethyl 2-cyanoacrylate polymer, the presence of the additional nitrile group had the unintended but desirable effect of shifting the strong CO absorption to higher frequencies, moving it away from interfering banknote absorptions. This enabled fingermark contrast to be achieved even against the intaglio printing on the banknotes.     

Visualization of latent fingerprints using fluorescence lifetime imaging on paper emitting strong fluorescence

Latent fingerprints were successfully visualized using fluorescence lifetime imaging (FLIM) on paper which emits strong fluorescence with a lifetime close to that of fingerprints and thus from which it is difficult for time-resolved spectroscopy to visualize fingerprints. Latent fingerprint samples on paper were excited using a 450 nm or 532 nm nanosecond pulsed-laser, and time-resolved fluorescence images were obtained at a delay time of 6–16 ns in intervals of 1 ns, to the excitation pulse. The excitation beam was expanded using a lens, and the fluorescence from the fingerprints was captured using an intensified CCD camera. Because of the large fluorescence intensity of the background paper of approximately two to four orders of magnitude larger than that of the fingerprint, the fingerprint was not visualized on each fluorescence image by time-resolved spectroscopy. However, the fingerprint was visualized in a FLIM image constructed using a series of the fluorescence images for the case with the fluorescence intensity of the background paper being four orders of magnitude larger than that of the fingerprint. The difference in fluorescence lifetime in the FLIM image of the visualized fingerprint and background paper was in the order of 0.1 ns, which was an order of magnitude smaller than the inherent fluorescence lifetime of a few nanoseconds for the fingerprints and paper. It was demonstrated that, at a background fluorescence intensity with a certain order of magnitude larger than that of fingerprints, FLIM has the potential to visualize latent fingerprints which cannot be visualized by time-resolved spectroscopy.     

Infrared spectroscopic imaging for noninvasive detection of latent fingerprints

The capability of Fourier transform infrared (FTIR) spectroscopic imaging to provide detailed images of unprocessed latent fingerprints while also preserving important trace evidence is demonstrated. Unprocessed fingerprints were developed on various porous and nonporous substrates. Data-processing methods used to extract the latent fingerprint ridge pattern from the background material included basic infrared spectroscopic band intensities, addition and subtraction of band intensity measurements, principal components analysis (PCA) and calculation of second derivative band intensities, as well as combinations of these various techniques. Additionally, trace evidence within the fingerprints was recovered and identified.     

A scanning beam time-resolved imaging system for fingerprint detection

A highly sensitive confocal scanning-beam system for time-resolved imaging of fingerprints is described. Time-resolved imaging is a relatively new forensic procedure for the detection and imaging of latent fingerprints on fluorescent substrates such as paper, cardboard, and fluorescent paint. Ordinary fluorescent imaging of latent fingerprints on these surfaces results in poor contrast. Instead, the specimens are treated with a phosphorescent dye that preferentially adheres to the fingerprint which allows time-resolved discrimination between the fingerprint phosphorescence and the background fluorescence. Time resolved images are obtained by synchronizing the digital sampling of the specimen luminescence with the on-off cycle of the chopped illumination beam. The merit of this technique is illustrated with high contrast images of fingerprints obtained from the fluorescent painted surface of a Coke can.     

利用CdSe巯基乙酸溶液显现水浸客体表面潜手印

目的研究水浸客体表面潜指纹的显现方法;方法利用CdSe巯基乙酸溶液显现被水浸泡过的黄色封箱胶带、黑色塑料袋、玻璃等常见非渗透性客体上的潜手印,讨论影响水浸非渗透性客体上潜手印显现效果的各种因素,并与传统方法进行比较,初步探讨了CdSe巯基乙酸溶液显现水浸非渗透性客体表面潜手印的方法;结果使用巯基乙酸包覆CdSe纳米复合材料显现潜在手印,使每分子纳米复合材料外表包覆足够数量的羧基,则可以提高它同手印残留物的结合能力,从而得到更高清晰度、更高分辨率的手印显像;结论巯基乙酸包覆CdSe纳米复合材料可以很好的显现水浸塑料、胶带等表面潜指纹。     

Luminescent visualization of latent fingerprints by direct reaction with a lanthanide shift reagent.

The utilization of the lanthanide shift reagent tris (6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium (III) [Eu(fod)3] as a simple one-step reagent for the luminescent visualization of latent fingerprints has been investigated. UV excitation of Eu(fod)3-treated prints, achieved by using a hand-held UV lamp or a Polilight, results in an orange emission at 614 nm. Time-resolved imaging is not required for visualization. Visualization of latent fingerprints on paper under the conditions used, although good, was found to be inferior to that obtained by standard DFO (1,8-diazafluoren-9-one) treatment, whereas visualization of prints obtained on aluminum drink cans and galvanized iron proved superior to that obtained by Superglue/panacryl treatment. Eu(fod)3 treatment can also be used first without compromising subsequent ninhydrin or DFO treatment, making it a 'nothing-to-lose" reagent.     

A further study to investigate the detection and enhancement of latent fingerprints using visible absorption and luminescence chemical imaging

This study investigated the application of chemical imaging to the detection of latent fingerprints using the Condor macroscopic chemical imaging system (ChemImage Corp., Pittsburgh, USA). Methods were developed and optimised for the visualisation of untreated latent fingerprints and fingerprints processed with DFO, ninhydrin, cyanoacrylate, and cyanoacrylate plus rhodamine 6G stain. The results obtained with chemical imaging were compared to the detection achieved using conventional imaging techniques. The Condor significantly improved the detection of many prints, especially those that might be considered poor quality or borderline prints. Prints on newspaper treated with ninhydrin and DFO, and prints on white and yellow paper treated with ninhydrin, benefited the most from chemical imaging detection. In many cases, fingerprints undetectable using conventional imaging techniques could be visualised with chemical imaging. Ridge detail from untreated prints on yellow paper was also detected using the Condor. When prints of high quality were examined, both detection techniques produced quality results. The results of this project demonstrate that chemical imaging offers advantages over conventional visualisation techniques when examining latent fingerprints, especially those that would be considered difficult, such as weak prints or prints on surfaces that produce highly luminescent backgrounds. Standard testing procedures for the detection and enhancement of fingerprints by chemical imaging are presented and discussed.     

Time is Money or Money is Time? A Rapid Operational Sequence for Detecting Fingermarks on Polymer Banknotes

Banknotes are often found in high-profile crimes such as armed robberies, bribery, and terrorist activity. However, such exhibits present a challenge to forensic operatives regarding fingermarks development, due to their mass quantities, potential for fingermarks on both sides, and their unique complex background in terms of color, irregular patterns, and topography. Hence, the standard development protocols become inefficient, due to the difficulty in achieving high contrast images over the background. This study focused on finding an operational sequence that would minimize the time of work on polymer banknotes, in terms of both development and image processing. Thirty-two fingermarks were developed by vacuum metal deposition (VMD), black magnetic powder, and cyanoacrylate fuming (CA) followed by visualization and imaging by reflected short-wave UV (RUVIS) (96 in total), showing a distinct advantage to the CA and RUVIS imaging over the other two techniques with a 75% success rate in the dark and high background regions, due to its physical principle which neutralizes high background interference. The images were then scanned by the automatic fingerprint identification system (AFIS) to test its ability to correctly differentiate false background features from real ones, again, showing a superiority of the RUVIS with 63% of the total initial marked features, being real. Overall, the CA and RUVIS sequence was found to be an ultimate method for multiple, same-type surfaces, with the RUVIS capable of visualization and capturing of the images simultaneously, significantly reducing the time of development and image processing.     

Contactless Visualization of Latent Fingerprints on Nonporous Curved Surfaces of Circular Cross Section—A Statistical Evaluation on the Materials as Plane Mirror

A new contactless technique for latent fingerprint visualization on nonporous curved surfaces of circular cross section was introduced by Low et al. (1). The technique utilizes a plane mirror to convey the light rays toward the inspected surfaces for latent fingerprint visualization. This research activity came up as an extension of the previous study which utilized an aluminum plate as the plane mirror to illuminate the inspected surfaces. Dulling spray was used to increase the diffuse component of the reflective aluminum plate. However, the amount of dulling spray will affect the uniformity of the illumination on the inspected curved surfaces. In this study, a study on the new materials for the plane mirror was carried out. Coated aluminum, opal, and ground glass diffusers were selected as the new materials. The performance of the new materials was compared to the aluminum based on the quality of the captured images on various nonporous cylindrical surfaces. A statistical approach known as randomized complete block design was used to design the experiment. The quality of the captured images was obtained using Spectral Image Validation and Verification. Two‐way analysis of variance and Fisher's least significant difference test were used to analyze the quality of the images. From the results of the statistical analysis, coated aluminum has the best performance compared to aluminum, opal, and ground glass diffusers.     

The Effects of High Dynamic Range on Fingerprint Images Processed by Photoshop

High dynamic range (HDR) imaging is a function that combines five images with different exposures into a single image. This technique may provide fine ridge details of fingerprint images for forensic latent fingerprint examination. Therefore, viewing fingerprints under optimal conditions is of paramount importance. This paper analyzes HDR and non‐HDR photos by using the Michelson contrast formula. The Michelson formula will provide a measurement to determine whether better contrast between the background and print can be achieved using the HDR function and if the background color affects the quality of the images. Two hypothesis were tested: (i) the HDR image provides more details of fingerprints with a better tone, greater clarity, and contrast than a normally exposed image regardless of the background color; (ii) the background color does not affect the quality of HDR fingerprint images overall, but the multi‐color background may increase the contrast of HDR fingerprint images in some cases.     

Vapor-phase staining of cyanoacrylate-fumed latent fingerprints using p-dimethylaminobenzaldehyde

Contrasting or enhancing of cyanoacrylate ester-fumed latent fingerprints deposited on solvent-sensitive materials such as oil marker writings and rough surface materials such as unglazed earthenware is not easy by conventional dye solutions dipping or dye powder dusting. In this study, a new vapor-phase staining method using p-dimethylaminobenzaldehyde (DMAB) is proposed for staining such materials. DMAB has high volatility and selective absorbability to cyanoacrylate-fumed fingerprints, so that cyanoacrylate-treated samples can be easily stained by leaving them simply in a closed container along with DMAB crystals for 48-96 h at room temperature or in conjunction with the use of mild heating. The stained fingerprint could be excited by UV irradiation (365 nm), and the fluorescent fingerprint was photographed through a UV cut-off filter (420 nm). The new method achieved minimally destructive fluorescent staining for the solvent-sensitive samples and the rough surfaced samples.     

Genipin, a novel fingerprint reagent with colorimetric and fluorogenic activity, part II: optimization, scope and limitations

Genipin, a hydrolytic product of geniposide extracted from gardenia fruit, was thoroughly studied as a potential fingerprint reagent, and optimal conditions for fingerprint development have been determined. Latent fingerprints on paper items that have been treated with a non-ink running formulation containing 0.17% of the reagent, showed up as both colored and fluorescent images. On brown wrapping paper and on papers with highly luminescent backgrounds, genipin developed more visible and clearer prints than did classical reagents such as ninhydrin or DFO. Another potential advantage of genipin is that it is totally harmless and an environmentally friendly reagent.     

Effect of Aging and Surface Interactions on the Diffusion of Endogenous Compounds in Latent Fingerprints Studied by Mass Spectrometry Imaging,

The ability to determine the age of fingerprints would be immeasurably beneficial in criminal investigations. We explore the possibility of determining the age of fingerprints by analyzing various compounds as they diffuse from the ridges to the valleys of fingerprints using matrix‐assisted laser desorption/ionization mass spectrometry imaging. The diffusion of two classes of endogenous fingerprint compounds, fatty acids and triacylglycerols (TGs), was studied in fresh and aged fingerprints on four surfaces. We expected higher molecular weight TGs would diffuse slower than fatty acids and allow us to determine the age of older fingerprints. However, we found interactions between endogenous compounds and the surface have a much stronger impact on diffusion than molecular weight. For example, diffusion of TGs is faster on hydrophilic plain glass or partially hydrophilic stainless steel surfaces, than on a hydrophobic Rain‐x treated surface. This result further complicates utilizing a diffusion model to age fingerprints.     

Trace evidence dynamics of cocaine on banknotes: A comparison study of paper and polymer banknotes

It is well established that a large proportion of paper banknotes in circulation contain traces of cocaine. Being able to discriminate between the innocent transfer of illicit drug particles acquired through everyday interactions with surfaces such as banknotes, as opposed to transfer resulting from criminal activities can provide valuable intelligence that can inform an investigation. With many countries adopting polymer banknotes as legal tender, it is important to consider the transfer of cocaine from these surfaces as well as the retention of these particulates on polymer banknotes for evaluative interpretation in crime reconstruction. This comparison study assessed three contact variables (force, time, and rotation) on the transfer of cocaine particulates from paper and polymer banknotes onto a human skin proxy. The persistence of cocaine particulates was assessed through a realistic scenario which mimicked a cash transaction. Quantifiable amounts of cocaine were transferred onto the human skin proxy across all of the contacts assessed, with a greater transfer observed with contacts involving polymer banknotes and those contacts which involved rotation. Following extensive handling, cocaine persisted on both banknote types, with paper banknotes retaining larger amounts of cocaine than polymer banknotes. These findings show that cocaine can persist on both paper and polymer banknotes for extended periods of time following handling and is therefore available for transfer. This transfer then readily occurs, even when contact is brief and involves relatively small forces. A key distinction between the banknote types was that cocaine particulates are more likely to transfer from polymer banknotes due to the lower retention rate of particulates on this surface. Such insights can aid in evaluating the relevance of illicit drug particles identified on items or persons of interest in crime reconstruction approaches.     

Evaluation of Four Fingerprint Development Methods for Touch Chemistry Using Matrix‐Assisted Laser Desorption Ionization/Time‐of‐Flight Mass Spectrometry,

Four preparation techniques for MALDI/TOF mass spectrometry were compared to determine the ability to gather intelligence for investigations through the chemical analysis of latent fingerprints, defined as “touch chemistry.” Compatible fingerprint development processes used for identification along with new techniques are necessary to evaluate touch chemistry. Ten volunteers deposited fingerprints from solvent residues containing drugs and explosives onto microscope slides. The developers included (A) fingerprint powder, (B) MALDI matrix, (C) fingerprint powder and lifting, and (D) cyanoacrylate fuming with fingerprint powder. Qualitative identification was based on ion images and spectra. The highest average detection rates (88%) were found using methods A and B. Methods C (52%) or D (18%) had limited success. Results demonstrate the importance of imaging coupled to extracted mass spectral data in detecting analytes in deposited fingerprints. Overall, the results suggest continued development of touch chemistry applications could prove useful for gathering intelligence and forensically relevant information.     

Fingerprint detection on counterfeit US dollar banknotes: the importance of preliminary paper examination

Two seizures of counterfeit 100 US dollar bills related to the same indicative number were submitted for processing of latent fingerprints. On one group of notes, identifiable fingerprints could be detected by the routine application of amino acid reagents. In the second case, this technique gave no results, even on deliberately deposited prints. Fingerprints could be revealed, however, by cyanoacrylate fuming followed by magnetic powder. Comprehensive paper analysis showed that banknotes from both seizures differed remarkably by chemical composition as well as paper macroscopic properties. The difference in surface free energy (related to surface tension) of the banknotes in the two groups seemed to be the major factor responsible for the great variance in fingerprint detectability.     

A Modified Electrostatic Adsorption Apparatus for Latent Fingerprint Development on Unfired Cartridge Cases

Visualization of latent fingerprints on metallic surfaces by the method of applying electrostatic charging and adsorption is considered as a promising chemical‐free method, which has the merit of nondestruction, and is considered to be effective for some difficult situations such as aged fingerprint deposits or those exposed to environmental extremes. In fact, a portable electrostatic generator can be easily accessible in a local forensic technology laboratory, which is already widely used in the visualization of footwear impressions. In this study, a modified version of this electrostatic apparatus is proposed for latent fingerprint development and has shown great potential in visualizing fingerprints on metallic surfaces such as cartridge cases. Results indicate that this experimental arrangement can successfully develop aged latent fingerprints on metal surfaces, and we demonstrate its effectiveness compared with existing conventional fingerprint recovery methods.     

NFIQ 2.0用于指纹质量控制的可行性及方法

目的测试NFIQ 2.0标准计算指纹质量评分模块在活体采集和油墨捺印指纹质量控制上的可靠性,研究利用NFIQ 2.0指纹分值综合判断指纹质量的可行性和在实际工作中的使用方法。方法一是利用NFIQ 2.0模块接口程序结合VS2015 C#编程语言制作指纹质量评分软件。二是记录20张指纹图片放置在采集框上、下、左、右、中五个位置时NFIQ 2.0的分值,计算平均偏差、最大偏差和相对偏差。三是对在指纹数据库中随机选出的1334枚活体采集和油墨捺印指纹(8位灰度、500 dpi BMP格式指纹图片)进行评分,将得出的分值与通过人工检查该1334枚指纹在指纹系统中自动提取的特征所计算的特征准确率,形成线条图并制作拟合线,通过线条图和拟合线研究NFIQ 2.0分值与特征准确率之间存在的关系。结果从平均偏差、最大偏差和相对偏差分析,指纹图片放置位置对NFIQ 2.0分值的影响很小。利用线条图和拟合线进行统计时,NFIQ 2.0分值与特征准确率之间呈现出一定的对应关系,NFIQ 2.0分值高的指纹,系统自动提取的特征准确性相对较高,反之相对较低。并且,分值在41~100之间时,特征准确率稳定在80%以上。结论NFIQ 2.0标准计算指纹质量评分模块可以用于大批量活体采集和油墨捺印指纹的辅助质量检测,在实际工作中可将NFIQ 2.0模块嵌入活体采集软件和指纹系统档卡扫描中,设定合理的阈值,对提高指纹采集的质量检测效率和提升指纹采集质量将有较大帮助。