Can Lip Prints Change Overnight?: A Study of Lip Print Stability Across Day and Night as a Forensic Identification Tool

Abstract Aim Lip prints have long been considered unique and stable over time, causing a boost of cheiloscopy research to understand the potential of lip prints for forensic identification. While studies looking at lip print stability over time are common, this study investigates the stability based on the day and night phenomenon. Methodology Lip prints were taken from 200 participants from the campus population using the standardised paper technique, wherein lip prints were made on A4 papers then digitised using a high- resolution scanner. Lip prints similarity percentage were formed by comparison of the prints collected at the morning and evening, then analysed using Contrastive Language-Image Pre- training (CLIP) image analysis model. Statistical analysis included repeated-measures ANOVA to compare the lip print similarity percentage obtained at Day 1, Day 7 and Day 14. Intra-class correlation coefficient (ICC) is used to test the reliability of the CLIP model to analyse lip print images. Results Repeated measures ANOVA indicated significant variation in lip prints similarity percentage obtained at Day 1, Day 7 and Day 14. The intraclass correlation coefficient (ICC) was rated 0.649, between fair and good. Conclusion The study concludes that lip print morphology may not be as stable over short time intervals as previously assumed, and this variability should be considered in forensic evidence collection. Keywords Cheiloscopy, Lip Prints, Deep Learning, Digital Analysis, ICC