The non-contact detection and identification of blood stained fingerprints using visible wavelength hyperspectral imaging: Part II effectiveness on a range of substrates

Abstract

Biological samples, such as blood, are regularly encountered at violent crime scenes and successful identification is critical for criminal investigations. Blood is one of the most commonly encountered fingerprint contaminants and current identification methods involve presumptive tests or wet chemical enhancement. These are destructive however; can affect subsequent DNA sampling; and do not confirm the presence of blood, meaning they are susceptible to false positives. A novel application of visible wavelength reflectance hyperspectral imaging (HSI) has been used for the non-contact, non-destructive detection and identification of blood stained fingerprints across a range of coloured substrates of varying porosities. The identification of blood was based on the Soret γ band absorption of haemoglobin between 400 nm and 500 nm. Ridge detail was successfully visualised to the third depletion across light coloured substrates and the stain detected to the tenth depletion on both porous and non-porous substrates. A higher resolution setup for blood stained fingerprints on black tiles, detected ridge detail to the third depletion and the stain to the tenth depletion, demonstrating considerable advancements from previous work. Diluted blood stains at 1500 and 1000 fold dilutions for wet and dry stains respectively were also detected on pig skin as a replica for human skin.

A comparison of visible wavelength reflectance hyperspectral imaging and Acid Black 1 for the detection and identification of blood stained fingerprints

“…The approach carried out by our research group indicated a higher sensitivity and specificity for the detection and identification of blood stains over previously proposed methods [3]. Recent research has since successfully demonstrated the application of this technique for the detection, identification, and visualisation of ridge detail in blood stained fingerprints deposited on white ceramic tiles [19] and a range of other substrates commonly encountered at scenes of crime [20]. To date there has been no comparison between HSI and existing chemical enhancement methods, such as Acid Black.…”

“…The HSI system used in this study was the same setup detailed in [3] and [19,20], consisting of a liquid crystal tuneable filter (LCTF) coupled to a 2.3 megapixel Point Grey camera and a light source for scene illumination. The light source was comprised of two 40W LEDs; one violet giving an output at 410nm and one white giving an output between 450 and 700 nm.…”

“…The hyperspectral reflectance measurements were made following the method detailed in [3] and [19,20]. A reference image (R 0 ) was obtained using a blank ceramic tile.…”

“…One of the key issues involving the optical analysis of fingerprints is to ensure sufficient ridge detail is captured to allow for comparison of crime scene marks against fingerprints from a suspect. A comparison of existing enhancement methods against HSI would allow for the sensitivity of the setup to be measured, which is necessary if HSI is to be further developed [20]. In this study a novel application of hyperspectral imaging (HSI) is used for the non-contact, non-destructive detection and identification of blood stained fingerprints on white tiles both before and after wet chemical enhancement using Acid Black 1.…”

“…Results potentially indicate a significant step towards a reliable method for both non-destructive blood identification and the detection of ridge detail in blood stained fingerprints, both before and after chemical enhancement. This work is following on from [19,20], where hyperspectral imaging was demonstrated for the first time to detect, identify, and visualise to a sufficient resolution the ridge detail of blood stained fingerprints across a wide range of substrates. The research presented in this paper again demonstrates the potential of HSI, through a comparison of the successful nondestructive detection and identification of blood stained fingerprints against Acid Black chemical enhancement.…”