Estimation of bloodstain age on synthetic leather from photographs and analysis using MATLAB

Abstract

Bloodstains are among the most common forms of physical evidence found at crime scenes. Estimating the age of a bloodstain is an important and intriguing aspect of forensic investigation. This study investigates the estimation of bloodstain age on two types of synthetic leather PU (polyurethane) and PVC (polyvinyl chloride). A volume of 100 microliters of blood was applied to the surface of each material and stored under three different environmental conditions: shaded (indoor), natural outdoor, and UV-exposed environments. Observations were made at the following time intervals: immediately after deposition, 15 minutes, 30 minutes, 45 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 24 hours, 48 hours, 72 hours, 96 hours, 120 hours, 144 hours, and 168 hours. At each time point, samples were photographed, and the RGB color values were analyzed using MATLAB software. The results showed that the average red (R) value decreased rapidly within the first 4 hours for both PU and PVC synthetic leather under all three conditions. A graph was created to illustrate the relationship between average red values and time on PU synthetic leather. It was observed that the red values under shaded and natural outdoor conditions showed a similar decreasing trend. By the final time point, the lowest red value was recorded in the UV-exposed condition. For PVC synthetic leather, the average red values in all three environmental conditions showed a comparable decreasing trend. The data were then analyzed using linear regression, separated into two models: a short-term model (from initial deposition to 45 minutes) and a long-term model (from 1 hour to 4 hours). Both models yielded correlation coefficients close to 1, indicating strong reliability and the potential application of this method for estimating the age of unknown bloodstains.