基于过程解析法的同机添加打印文件鉴别方法

Identification of Added Printing from Same Printer Based on Process Analysis

利用喷墨打印机二次添加打印,特别是同机添加打印变造文件,是文件检验工作中的难题。喷墨打印机采用串行接字方式,内部结构复杂,喷嘴数目多,同一型号打印机又有多种质量模式。因此,在打印图文上往往留有较多的打印特征,如对接重叠线、对接错位线、横向白线、卫星墨点、墨点错位等。分析爱普生、惠普、佳能三个品牌的20台喷墨打印机不同质量模式的打印文件,发现这些特征重复再现频率较高,不同台打印机打印文件特征差异较大,同一台打印机在不同质量模式下特征出现的位置也不尽相同。通过提取打印文件上的打印特征,分析字车运行方向和打印图文pass数值,分解打印过程并制作检验图谱,判断打印文件的可疑区域是否符合打印规律,为确定二次添加打印提供帮助,提升检验过程的规范性、检验意见的准确性和结果依据的可读性。

At times,the added printing occurs from the same inkjet printer to falsify document,posing difficulty for questioned document examination.The inkjet printer adopts serial line-connection word-printing mode,usually having features of complicated internal structure,numerous nozzles and multiple quality modes with its same model/machine.Therefore,there are many printing characteristics harbored with the printed documents(photos or texts),e.g.,the overlapping band,abutting malposition,vertical misaligning,horizontal white line,satellite drops and position-error droplets,all of which can certainly leave clues or suggestions for forensic examiners to identify or distinguish to get potential evidence.With 20 inkjet printers of different quality modes from Epson,HP and Canon brands,the relevant documents were printed for analysis,demonstrating that many characteristics mentioned above are of high-frequency recurrence.Different printers of identical brand bring forth documents of quite discrepant characteristics,and even same printer procreates position-alterant characteristics on selection of its different quality modes.Through analysis of the characteristics exposed from the documents made above,the printing process was parsed into the involving printer’s operation:the running direction of the printing carriage ruled under the pass value of the printed photo or text,the printing course helping contrive the continuous specific examination procedure/map.Thus,the judgement was concluded on whether the suspicious areas of the printed documents conform to printing rules,hence drawing a determination about presence/absence of second added printing.The discoveries here will lead to improving the standardization of inspection process,the accuracy of identification opinions,the readability of results and the verifiability of evidence.Usually,inkjet printers equipped with model-same printing heads in performing with the same or similar operating rules are not easy/intentional to change by ordinary users.Consequently,the identification of inkjet-printed documents will be provided with great support through collecting the data about the number and arrangement of nozzles from different types of printing heads and establishing an examination map library of operating rules for printing carriage under various print-driver programs.