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Introduction

The concept of document examination is constantly changing due to the ongoing advancements in digital technology associated with printers. Text or images existing in a document can be digitally manipulated easily and multiple copies can be prepared. The authenticity and integrity of such documents is an important aspect in forensic document analysis, which cannot be ignored. Thus, it is essential to have detailed knowledge about the class and individual characteristics of printed and copied documents. This may help a forensic document examiner to prove whether a document is original or just a colored copy [1-3]. This knowledge may also help to link two or more documents and to conclude whether these two documents originated from a single printer or multiple printers were used for their preparation [4-6]. Documents can also be differentiated on the basis of the physical characteristics of printer used to print them [7-9].

Thus, this study has been carried out to determine the differences between the characteristics of original documents and their scanned colored copies. Original documents were scanned and their colored copies were produced using inkjet printers and laser printers. A stereomicroscope (Nikon SMZ800N) was used for analysing and comparing various physical characteristics.

Materials and Methods

Sample Preparation

Different types of original documents were collected on request and are listed in Table 1 along with their sample ID. Each original document was scanned and printed using five laser printers and four inkjet printers. Table 1 also indicates the specifications of various printers used for sample preparation. The phrase “FOR EXPERIMENTAL PURPOSE” was super-scribed on each scanned document before printing it. The dimensions of some documents were adjusted by printer settings to make them fit on the sheets on which they were printed. The prints were obtained on plain A4 size sheets in case of inkjet printers and glossy sheets were used for laser printers. The samples were collected in two phases over the course of two months. However, in first phase, one document (MSD) was not printed by an inkjet printer (E380) due to its large size as compared to the scanner. This reduced the sample size to 71 (8 × 9 – 1). In second phase, two printers (DC2020 and CN3010) were not in a working condition, further limiting the number of samples to 55 (8 × 7 – 1). Hence, in total 134 samples (126 copies + 8 original) were examined.

A separate 9 samples were prepared in similar manner for a blind test of the method. Out of these nine samples, five were printed using a laser printer. While the rest four samples were printed using inkjet printer. The samples were randomly presented to the lead author for evaluation and the identity of the samples was kept confidential until the evaluation was complete.

Analysis

All documents were rigorously analysed in two steps. The first step included a visual examination of document and the second step included a stereomicroscopic examination. The results were tabulated.

Visual Examination

All original documents and their respective copies were initially examined and compared on the basis of visual characteristics and irregularities present in the smooth surface of paper, followed by recording their pictures under oblique light to obtain maximum depth. Change in the dimensions, change in color, and indentation and embossment were analysed in the visual examination.

Stereomicroscopic Examination

The original documents and their respective colored copies were examined and compared under a Nikon (Tokyo, Japan) SMZ800N stereomicroscope with a maximum magnification of 2 × 10 × 8 X, and Nikon C-FLED2 LED light source was used at different angles with respect to the paper, in order to observe minute details present in the document. For analysis, images were captured using a Nikon DIGITAL SIGHT DS-U3 camera head and camera model DS-Fi2. The NIS-Element software (Nikon, Tokyo, Japan) was used to capture images. Analysis was done with extreme care at different magnifications. Various observations witnessed with the help of stereomicroscope under oblique lighting are as follows.

• Printing method and ink type
• Security features
• Printing characteristics and defects

Similarly, blind samples were analyzed for the aforementioned features, by following similar procedure. The outcomes were noted down and compared.

Results

Visual Examination

Following observations were made after visual examination of the original documents and their colored copies and tabulated in table 2 – table 7.

Change in Dimensions

On scanning and printing the original document, any of the three major changes were observed in the copied document, that is, the size of the copied document reduced, the size of the copied document remained same as the original document, or the size of the copied document increased. In case, the size of the copied document reduced or increased from the size of the original document, it was clearly observable in the visual examination and comparison. In addition to this, incomplete information such as cropped signatures, text and edges were also observed in all the three samples.

Changes in Color

Printing inks are broadly distinguished by the printing method in which they are utilized. The dyes and pigments present in the ink determine the color of the ink, its hue, strength, and transparency. On juxtapose comparison of original and copied documents, difference in colors was observed. Also, different printing methods used in copying resulted in different characteristic colors.

Indentation and Embossment

Indentation and embossment was present on various original documents, all of which disappeared in their respective copies. Embossment was observed mostly on the back side of the indented text or logo.

Stereomicroscopic Examination

Following observations were made after stereomicroscopic examination of the original documents and their colored copies and tabulated in table 2 – table 7.

Printing Method and Ink Type

Printing methods - In some of the original documents, printing characteristics of more than one printing method were observed. However, their respective colored copies indicated the use of only one printing method in the whole document.

Pen inks - In case of original documents, signatures were observed to be made up of a ball point pen ink or gel pen ink. However, the pen inks of signatures were printed in accordance with the printer used in the respective colored copies when observed under stereomicroscope.

Intersections - In original documents, where more than one printing method was utilized for printing, clear intersecting strokes were observed. Intersections were observed between printed text, images, handwritten signatures, etc. In contrast, intersections were absent in the colored copies and at certain places it blurred.

Security Features

Micro-printing - Micro-printing was the most common security feature observed in various original documents under stereomicroscope. It was absent in their respective colored copies as the scanner and printer could not replicate the micro-printing.

Watermark - In some of the original documents, printed watermarks were observed in the background. Under stereomicroscope it appeared as a pattern of fine dots or text of a particular color. However, the respective copies of original documents did not show such patterns or these were tampered.

Printing not visible to naked eye at the bottom - A specific pattern of dots (whose dot size was larger than the size of dots present in the background pattern) found in the words ‘COPY’, ‘ORIGINAL’, made of single color that was only visible under the stereomicroscope in original documents. Either it disappeared or changed microscopically in aspects of color configuration in the forged documents.

Indentation and embossment - Indentation and embossment of logo was observed under stereomicroscope on various original documents when observed with light at grazing angle. However, these disappeared in their respective copies.

Printing Characteristics and Defects

Sheen - In few original documents, when observed under oblique light, sheen was observed on the surface of text and logo. This may be due to raised printing of text or due to coating material. However, sheen was not observed in their respective colored copies.

Spacing between texts - When observed under stereomicroscope, a minute space was observed between some Gurumukhi letters in original documents of MDP. However, this space was not observed in their respective colored copies. The text appeared to be continuous.

Printing defects - A number of printing defects depending on the scanner and type of printer used to print the documents, such as spur marks, extra deposition of ink droplets or toner particles, poor quality printing, mechanical defect, and glass platen defects were observed in the copied documents. However, no such defects were present in their respective original documents. Apart from this, individual features of inkjet printing (Table 8) and laser printing (Table 9) were observed. These defects were helpful to individualise and identify the make and model of the printer used for the production of the forged document.

Blind Test

The blind test samples were also examined using the same methodology. After careful examination of all the blind samples, correct interpretation was made for 100% samples. Hence, the results of blind test were similar to the results in this study. This validated the methodology and the results obtained in the study.

Discussion

A number of physical characteristics were considered which proved extremely useful for the comparison of original documents with their copies. From the results, it is evident that the changes in dimensions are enforced while copying an original document, which can be clearly observed in the copied document. In addition to this, it came out to be apparent that it is very difficult to copy the exact color, indentations, embossments and micro-printing present on the original documents. Although, the copied document may look similar on viewing with naked eyes, but a clear picture can be formed with the help of a stereomicroscope and juxtapose comparison. Previously, [1, 2, 5, 16] reported various defect marks, physical features, spur marks, and satellite droplets in their individual studies for the purpose of classification and identification of inkjet printouts. Referring to the above studies, the study has also utilized features such as satellites, spur marks, lining, and feathering for the identification and comparison of inkjet printouts. Further, [4, 5, 7, 9, 14, 15, 17] Arbouine et al. (1994), determined the source of electrostatically photocopied and laser printed documents on the basis of various physical characteristics and defect marks present on the printouts. In addition, [4] reported the use of image processing tools for examination of computer manipulated documents. All such general and individual characteristics like counterfeit protection system (CPS) code, toner particles, specific deposition pattern, and defects marks have been utilized for the examination and comparison of original documents and their respective copies.

Conclusion

The study demonstrated the competency of stereomicroscope in the analysis of physical characteristics of original documents as well as their colored copies. Characteristics including change in dimensions, change in color, embossment, indentations, pen ink, number of printing methods used, micro-printing, background details, defects, intersections, sheen, spacing, and individual features of printing method(s) were examined using Nikon SMZ800N stereomicroscope. The examination and comparison was performed between original documents and scanned copies of original documents. This study helped in determining sufficient physical characteristics of documents for proving their authenticity by utilising stereomicroscope. A stereomicroscope was used because this microscope is mostly used by document examiners in forensic science laboratories in India. It proved to be an easy, reliable and non-destructive method for analysis and comparison of documents.