Size influence on shape of handwritten characters loops

Area of Science:

• Forensic Science
• Graphology
• Biometrics

Background:

• Forensic handwriting analysis often encounters documents with varying writing sizes.
• The assumption of shape invariance in handwritten loops across different sizes is critical for accurate comparisons.

Purpose of the Study:

• To investigate the hypothesis of shape invariance for handwritten closed loops (a, d, o, q) when size is increased.
• To determine if loop shape modifications due to size changes affect writer identification in forensic handwriting examination.

Main Methods:

• Applied a Fourier methodology to analyze 2325 small and 692 enlarged handwritten loops from 13 writers.
• Writers produced letters at their usual size and approximately three times larger.

Main Results:

• Enlarged loops became significantly rounder and less slanted, indicating shape modification with size increase.
• High writer discrimination (>90%) was achieved using enlarged loops, but comparing enlarged to small loops resulted in ~50% misclassification.
• Shape invariance of handwritten loops across size variations was not supported.

Conclusions:

• Differences in loop shape between questioned and known documents may result from size variations, not necessarily different writers.
• Forensic handwriting experts should exercise caution when interpreting loop shape differences due to size.
• Requesting reference samples of similar writing size to the questioned document is crucial for accurate loop comparisons.