Variability of stamp impression measurements under different apposition conditions

Abstract

When a forensic document examiner obtains differences in size measurements between a questioned and reference stamp impressions, it may be difficult to assess whether such findings might be due to the use of the same stamp in different apposition conditions or are due to the use of different stamps. To address this issue, the present work has studied the variability of size measurements of stamp impressions apposed in various (pressure, humidity and temperature) conditions. Different stamps were also used to evaluate the influence of the fabricant, the matrix (photopolymer or rubber) and the inking type (selfinking and handstamp). While statistical tests sometimes indicated differences in the results, the measurement distributions overlapped for all kind of conditions (same stamps, different stamps), except for the two stamps produced by different manufacturers. Based on the findings of this study, a difference above 0.09 cm would support the hypothesis that two different stamps were used to produce the impressions. However, size differences below 0.09 cm were also encountered for impressions made using different stamps. The maximal size difference was actually measured for two stamps produced by different manufacturers (up to 0.29 cm).

Interpol questioned documents review 2019–2022

“…Stamps have been in use for thousands of years for all forms of business and social use and continue to be important globally in travel and identity documents, as well as regionally with course-of-business documents, Over the period of this review 11 articles [ [503] , [504] , [505] , [506] , [507] , [508] , [509] , [510] , [511] , [512] , [513] ] have been published on this topic, as well as seven conference presentations [ [514] , [515] , [516] , [517] , [518] , [519] , [520] ].…”

“…Rulli et al [ 504 ] compared measurements of stamp impressions made to different apposition and environmental conditions and found no significant differences. They concluded that: “Differences larger than 0.09 cm supported the hypothesis that two different stamps were actually used.” The difference could reach up to 0.29 cm when stamps from different manufacturers were used.…”