Fingerprints have great discriminatory power and are one of the most important and commonly encountered evidences at the scene of crime (SOC) (Thakar and Sharma 2016; Vij 2001). Due to their unique, immutable, and classifiable nature, fingerprints have been universally accepted as a means of personal identification since centuries. The questioned and specimen fingerprints are matched at three levels (Anthonioz et al. 2011; Ashbaugh 1999; Ashbaugh and Houck 2005; Jain et al. 2006; Liu et al. 2020; Maltoni et al. 2009; Pankanti et al. 2002; Stosz and Alyea 1994). The first level of fingerprint matching deals with macrofeatures (Jain et al. 2006), i.e., pattern type, ridge count, core, delta, and orientation. Level two consists of matching the relative nature and position of ridge characteristics (Galton’s minutiae) (Labati et al. 2018; Preethi et al. 2012). Level three involves the use of intra-ridge details (Kryszczuk et al. 2004) or microfeatures (Ashbaugh 1999; Gupta et al. 2008) such as sweat pores, edge contours, friction ridge width, dots, incipient ridges, creases, and scars (Ashbaugh and Houck 2005; Jain et al. 2006).
Fingerprints retrieved from the SOC can be complete or partial (fragmented). In case of the former, identification process, i.e., analysis-comparison-evaluation and verification (ACE-V), is relatively simple to conduct. However, the latter poses many problems mainly due to insufficient landmarks or level two details, unspecified orientation, and non-linear distortion (Gupta and Sutton 2010). Moreover, the print may be deposited from any other part of the hand than the finger tips (Ashbaugh 1999). Poroscopy, the specialized study of sweat pores found on the papillary ridges of the skin, can be especially useful in such cases (Ashbaugh and Houck 2005; Bindra et al. 2000; Cai et al. 2017; Gupta and Sutton 2010; Lee et al. 2014; Nagesh et al. 2011; Oklevski 2011; Park et al. 2016; Zhao et al. 2010a, 2010b).
The science of poroscopy was developed by Dr. Edmond Locard of Lyon, France, in 1912 (Ashbaugh 1999). Locard stated that like ridge characteristics, pores are permanent, immutable, and unique in nature and can aid in identification. He further proposed that 20–40 sweat pores in agreement are mathematically sufficient to prove the identity (Ashbaugh 1999). Sweat pores can be analyzed on the basis of the following features namely, number (per unit area and per unit length), shape, size, position (middle or periphery), type (closed, open on the one end, and open on both ends), and inter-distance.
The use of pore-to-pore distance for individualizing fingerprints has been effectively suggested by many studies (Anthonioz et al. 2011; Ashbaugh 1999; Liu et al. 2020; Monson et al. 2019; Oklevski 2011; Oktem et al. 2015; Parsons et al. 2008). However, no study has demonstrated the same using empirical data. When a pore undergoes distortion (due to pressure), it stretches (owing to the elasticity and compression of the skin), which results in change in its shape, size, and type (closed, open on the one side, and open on both sides). However, the inter-distance remains more or less the same. This is because the distance between pores is very minute (in μm); thus, multiple pores, on the same or different ridge(s), will be influenced simultaneously. Hence, pore inter-distance, with respect to each other, i.e., from the center of one pore to the center of the adjacent pore will remain more or less the same (within acceptable reproducible limits, i.e., with 5% confidence level in analytical work) for every individual. This forms the hypothesis of the present study.
In the present research work, an attempt has been made to study the reproducibility of two pore attributes namely, area and inter-distance (angle has also been taken into consideration), in fingerprints recorded over a period of ten consecutive days on two surfaces, i.e., glass and sticky side of adhesive tape, due to their increased use in day-to-day life. Moreover, the authors wanted to observe pore details on one porous and non-porous surface each hence, glass (non-porous) and sticky side of adhesive tape (porous) were selected. As far as we are aware, no prior research has attempted to evaluate pore parameters on the sticky side of adhesive tape.