Distortion in fingerprints: a statistical investigation using shape measurement tools

Area of Science:

• Forensic science
• Biometrics
• Friction ridge analysis

Background:

• Friction ridge impression appearance is influenced by surface type and deposition pressure.
• Quantifying these alterations is crucial for forensic applications.
• Understanding systematic changes aids in impression interpretation.

Purpose of the Study:

• To statistically characterize changes in friction ridge impressions due to substrate and pressure.
• To determine the magnitude and nature of alterations in fingerprint appearance.
• To assess the reliability of fingerprint transfer across different conditions.

Main Methods:

• Geometric morphometric techniques were employed for statistical characterization.
• Fingerprints were collected from multiple volunteers under varying pressure levels (heavy, normal, light).
• Impressions were made on diverse substrates including computer paper, soft gloss paper, 10-print card stock, and retabs.

Main Results:

• Different substrates and pressure levels induced minor, systematic changes in fingerprint appearance, approximately one ridge width.
• No detectable alterations in the random variability of prints were observed in relation to pressure or substrate.
• Fingerprints demonstrated reliable transfer across all tested conditions.

Conclusions:

• Friction ridge impressions are reliably transferred irrespective of the substrate or pressure applied.
• The observed changes in appearance are minimal and do not significantly impact the integrity of the impression.
• This study confirms the robustness of fingerprint evidence in forensic investigations.