Pattern recognition in a database of cartridge cases

1. ABSTRACT On the market several systems exist for collecting spent ammunition for forensic investigation. These databases store images of cartridge cases and the marks on them. The research in this paper is focussed on the different methods of feature selection and pattern recognition that can be used for comparison. For automatic comparison of these images it is necessary to extract firstly the useful parts of the images. On databases of 2000 images several preprocessing steps have been tested and compared. The results and methods, which have been implemented, are presented. 2. INTRODUCTION In the forensic science laboratory in the Netherlands a research study has been done for automated comparison algorithms of cartridge cases. This study was a part of evaluating the different systems, which exist on the market for databases of cartridge cases and bullets. These systems are Drugfire and IBIS. When a firearm is loaded and fired the mechanisms and part in the firearm which come into contact with the cartridge case or bullet cause impressions and striations that can be characteristic for the firearm being used. The striation marks on bullets are caused by the irregularities in the gun barrel as well as larger and more distinct land and grooves of the rifling. The cartridge case ejected will also have marks, which are caused by the firing pin, the breech face as the cartridge is repelled back in the breach by the force of rifling. The feeding, extraction and ejection mechanisms of the firearm will also leave characteristic marks. In the forensic science laboratory these marks on cartridge cases and bullets are compared with the test fired ones. Often the cartridge case is the most important forensic specimen in the identification of weapons, as bullets are commonly deformed by the impact. The examiner can also determine based on class characteristics what kind of firearm or which make and model has been used. This study handles the different approaches that can be used for comparison on image databases of breach face and firing pin marks. Further we have some other ideas which can be used in these systems for comparison.