Standard Guide for Printing Method Effects

on Facial Comparisons

OSAC 2021-N-0025

Standard Guide for 

Printing Method Effects on 

Facial Comparisons

Facial Identification Subcommittee

Digital/Multimedia Scientific Area Committee

Organization of Scientific Area Committees (OSAC) for Forensic Science
Standard Guide for Printing Method Effects

on Facial Comparisons

DRAFT 2

Draft OSAC Proposed Standard

OSAC 2021-N-0025

Standard Guide for Printing Method Effects

on Facial Comparisons

Prepared by 

Facial Identification Subcommittee

Version: 1.0

May 2021

Disclaimer:

This OSAC Proposed Standard was written by the Facial Identification Subcommittee of the 

Organization of Scientific Area Committees (OSAC) for Forensic Science following a process 

that includes an open comment period. This Proposed Standard will be submitted to a standards 

developing organization and is subject to change. 

There may be references in an OSAC Proposed Standard to other publications under 

development by OSAC. The information in the Proposed Standard, and underlying concepts and 

methodologies, may be used by the forensic-science community before the completion of such 

companion publications.

Any identification of commercial equipment, instruments, or materials in the Proposed Standard 

is not a recommendation or endorsement by the U.S. Government and does not imply that the 

equipment, instruments, or materials are necessarily the best available for the purpose.
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1 Rationale: Guidelines for performing facial comparisons 

2 using printed images in forensic environments.

3

4 Standard Guide for Printing Method Effects on Facial

5 Comparisons

6

7 This standard is issued under the fixed designation X XXXX; the number immediately following the designation indicates 

8 the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the 

9 year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. 

10

11 1. Scope

12 1.1 This guideline provides a basic overview of various printing processes as well as their 

13 characteristics and potential impacts on a facial comparison. 

14 1.2 The intended audience of this guideline anyone who contributes to a facial image 

15 comparison.

16

17 1.3 The values stated in Standard International (SI) units are to be regarded as standard. The 

18 values given in parentheses are mathematical conversions to non-SI units that are provided for 

19 information only. 

20

21 1.4 This standard does not purport to address all of the safety concerns, if any, associated 

22 with its use. It is the responsibility of the user of this standard to establish appropriate safety and 

23 health practices and determine the applicability of regulatory limitations prior to use.

24

25 2. Referenced Documents

26 2.1 ASTM Standards:

2.1.1 E2916 Terminology for Digital and Multimedia Evidence Examination.1 27

28 3. Terminology

29 3.1 Definitions:

30 3.1.1 Printed Image: A printed image is the production of a digital image on a substrate by 

31 a direct or indirect printing process.

1 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@asstm.org. For 

Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website.
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32 3.1.2 Dots per inch (DPI): In printing, DPI refers to the resolution setting of the printer and 

33 resolution capture for printed media. For example, a 1200DPI resolution printer will deposit a 

34 much higher density of ink per inch than a 300DPI printer. Use of DPI as a resolution term when 

35 scanning printed media will enable the use of post-scanning descreen software enhancement to 

36 more accurately reproduce the original artwork or image.

37 3.1.3 Lines per inch (LPI). A term in resolution setting in scanner software used for 

38 scanning original artwork for printing.

39 3.1.4 Pixels per inch (PPI): Measurements of the pixel density of an electronic image 

40 device, such as a computer monitor or camera. For example, a 1200PPI image will produce a 

41 higher quality image than a 300PPI image. Use of PPI as a resolution term is generally used with 

42 digitally capture images (i.e., photography). 

43 3.1.5 Samples per inch (SPI): A generic term that can include of DPI, LPI, and PPI. SPI is 

44 the measurement of the resolution, in particular the number of individual samples that are taken 

45 in the space of one linear inch. Scanner software may not allow for the use of SPI during image 

46 capture.

47 3.1.6 Substrate: A substrate in printing terms is a form of media on which a printed image 

48 is produced. A substrate, as referred to in this guideline includes gloss or matte paper, plastic, 

49 sensitized material, or polycarbonate. 

50 4. Summary of Practice

51 4.1 On occasion, a facial examiner will receive an image presented on a physically printed 

52 document. Printing processes will introduce artifacts or result in the loss of facial details. 

53 Consequently, an attempt to retrieve the original source image should be completed. 
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54 4.2 If the original source image cannot be retrieved, the facial examiner should have a basic 

55 understanding of common image printing processes. This will assist in identifying the potential 

56 printing effects and associated limitations that may affect the suitability to conduct a 

57 morphological facial image comparison.

58 5. Overview of Printing Processes

59 5.1 There are six printing processes that are commonly used to produce a printed facial 

60 image. Within this guideline, the printing methodology for each of these processes will be 

61 discussed in simple terms:

62 • Conventional and Digital Photographic

63 • Laser Toner

64 • Inkjet

65 • Thermal Transfer

66 • Dye Sublimation

67 • Laser Engraving

68 5.2 Potential Effects of a Printed Facial Image

69 5.2.1 The type of printer used to produce a facial image can result in a range of printing 

70 effects for consideration during a Facial Image examination. To demonstrate the differences in 

71 the printed output of the six printing processes, a comparative view of the printing processes 

72 appears below. For each of the six printing processes, the high-resolution image scans (1200
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73 DPI) of the eye area from a printed facial image are provided below to demonstrate the 

74 characteristics of each printing process and the potential effects of that process. 

75 See Appendix - Image Resolution in this Guideline for details on the images shown in this 

76 document. 
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 Photographic Laser Toner Dye Sublimation

 Inkjet Thermal Transfer Laser Engraving

77 FIG. 1 (Comparative view of each print process (high resolution image scan at 1200 DPI
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78 FIG. 2 Comparative view of the eye area for each print process (high resolution image scan at 1200

79 DPI)

80

Photographic Laser Toner

Inkjet Thermal Transfer

Dye Sublimation Laser Engraving
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81 6. Printing Definitions 

82 6.1 Conventional and Digital Photographic

83 6.1.1 Photographic prints are derived from either an image captured onto a light sensitive 

84 film or a digital image.

85 6.1.2 For conventional processes for color film, there are three light sensitive layers. The 

86 layers respond to exposure of Red, Green, and Blue light (RGB) to generate dyes that result in 

87 Cyan, Magenta, and Yellow (CMY) which are superimposed to form the final color in the 

88 finished print.

89 6.1.3 Modern photographic prints from a digitally captured image may use an Inkjet printer 

90 (with a photographic substrate) or more commonly Dye Sublimation for printing. 

91 6.1.4 The outcome of this process is that the printed image can display the following 

92 characteristics:

93 6.1.4.1 Only K (black) and white (basic substrate color) for monochrome images, or C 

94 (cyan), M (magenta), Y (yellow) if a three-color process has been used. In a three-color process 

95 K (black) may also be present but that is dependent on the combination of film and substrate 

96 used.

97 6.1.4.2 Can be printed on a range of papers from uncoated to resin coated paper and the 

98 appearance of the image may vary depending on whether the substrate has a matte or gloss 

99 finish. 
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100 6.1.4.3 The colors blend into each other producing continuous tonal images, often with no 

101 clear edge transition.

102

103 FIG. 3 Example of a Conventional and Digital Photographic print 

104 (Full facial image printed at 300 DPI and scanned at 1200 DPI for this guideline)

105 6.2 Laser Toner

106 6.2.1 Laser Toner printers are a type of non-impact printer that receive a digital image for 

107 printing followed by a laser transfer onto a photosensitive drum. Simultaneously, each color 
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108 toner is electrostatically charged to transfer onto the substrate and will combine with the 

109 positively charged areas of the drum to form the image. The negatively charged areas of the 

110 drum will repel the toner.

111 6.2.2 To transfer the image from the drum to a substrate, an electrostatic charge is used,

112 and the plastic particles of the toner are fused using heat to ensure adherence to the substrate 

113 surface.

114 6.2.3 The outcome of this process is that the printed image can display the following 

115 characteristics:

116 6.2.3.1 K (black) and white (basic substrate color) or different color toners i.e. C (cyan), M 

117 (magenta), Y (yellow), K (black).

118 6.2.3.2 Each color can be applied at different angles resulting in a pattern, known as a 

119 “rosette” pattern of dots.

120 6.2.3.3 Excess toner that results in visible toner dots surrounding the image area and also 

121 appearing in non-image areas of the substrate.

122 6.2.3.4 Under magnification, the toner appears to sit ‘on top’ of the substrate (as opposed to 

123 being absorbed into the substrate) and therefore can be scratched off.
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124

125

126 FIG. 4 Example of a Laser Toner print

127 (Full facial image printed at 300 DPI and scanned at 1200 DPI for this guideline)
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128 6.3 Inkjet

129 6.3.1 Inkjet, which is also known as bubble jet, is a printing process in which ink droplets 

130 are propelled from a small aperture onto the substrate. Inkjet printers use either on-demand (low 

131 pressure) or continuous (high pressure) ink propulsion from apertures to form an image on the 

132 substrate. 

133 6.3.2 The ink in this printer is electrostatically charged and propelled onto the substrate in a 

134 controlled formation based on the image dependent signals.

135 6.3.3 The outcome of this process is that the printed image can display the following 

136 characteristics:

137 6.3.3.1 K (black) and white (basic substrate color) or a four-color ink process i.e. C (cyan), 

138 M (magenta), Y (yellow), K (black).

139 6.3.3.2 Individual color droplets of ink are visible.

140 6.3.3.3 Excess ink resulting in dots visible around the printed image area (however they do 

141 not usually appear in non-image areas as in laser toner printing). 

142 6.3.3.4 Under magnification, the ink has a flat surface. For paper substrates, the ink bleeds 

143 into the paper fibers.

144 6.3.3.5 Irregularly shaped dots in an irregular pattern (i.e. splash like jagged edges can

145 sometimes be seen) and will not have a well-defined edge.
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146

147

148 FIG. 5 Example of an Inkjet print

149 (Full facial image printed at 150 DPI and scanned at 1200 DPI for this guideline)

150
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151 6.4 Thermal Transfer

152 6.4.1 Thermal Transfer printers are devices that use a combination of heated elements in a 

153 print head and a thermal reactive ribbon. The ribbon is a polyester base with wax, resin, or a 

154 combination of both wax and resin, and is generally referred to as containing ink.

155 6.4.2 The heating elements within the print head of this device are electronically controlled 

156 to contact the non-ink side of the ribbon, depending on image dependent signals. When and 

157 where required, the elements are heated and they melt the “ink” on the underside of the ribbon 

158 for transfer onto the substrate.

159 6.4.3 The outcome of this process is that the printed image can display the following 

160 characteristics:

161 6.4.3.1 K (black) and white (basic substrate color) or using a four-color process i.e. C (cyan), 

162 M (magenta), Y (yellow), K (black).

163 6.4.3.2 Under magnification, the “ink” has a flat surface. For paper substrates, the “ink” can 

164 bleed into the paper fibers.

165 6.4.3.3 Images have a dot like appearance.

166 6.4.3.4 A stepped effect to the edges of image.

167 6.4.3.5 There may be an overlap of the color frames.
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168

169

170 FIG. 6 Example of a Thermal Transfer print

171 (Full facial image printed at 300 DPI and scanned at 1200 DPI for this guideline)
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172 6.5 Dye Sublimation

173 6.5.1 Dye Sublimation printers are commonly used for continuous tonal ranges within a 

174 printed image. The term “sublimation” refers to the progression of a solid to a gaseous state 

175 without transitioning through the liquid phase. In this process, the printing color dyes are heated 

176 until they vaporize and reach the gaseous state, where the dye diffuses into the substrate and 

177 solidifies.

178 6.5.2 This type of printing process transfers colored dyes from a plastic ribbon onto 

179 specialized substrates. The main differences to other print processes discussed in this guideline 

180 are that the vaporized color dyes penetrate the surface of the substrate. The penetration into the 

181 substrate results in a gentle continuous gradation of tones at the edge of each pixel, instead of the 

182 obvious color changes seen in other printing processes.

183 6.5.3 The outcome of this process is that the printed image can display the following 

184 characteristics:

185 6.5.3.1 K (black) and white (basic substrate color) or using a four-color process i.e. C (cyan), 

186 M (magenta), Y (yellow), K (black).

187 6.5.3.2 Colors blend into each other producing continuous tonal images.

188 6.5.3.3 Used only on coated paper, plastic, or polycarbonate substrates.

189 6.5.3.4 Glossy appearance to the image.

190 6.5.3.5 Under magnification, the dye has a flat surface.
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191

192

193 FIG. 7 Example of Dye Sublimation print

194 (Full facial image printed at 300 DPI and scanned at 1200 DPI for this guideline)

195
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196 6.6 Laser Engraving

197 6.6.1 Laser Engraving is generally only used with polycarbonate or plastic substrates that 

198 predominately feature in identity documents, such as passports and identity cards. This process 

199 creates unique features and characteristics that are not present in other printing processes.

200 6.6.2 The composition of the polycarbonate or plastic substrate is multi-layered and the 

201 laser engraving enables various depths of carbonization in any of these layers. The depth of the 

202 engraving is dependent on the amount of energy used, and can result in raised print, flat print, or 

203 a combination of both raised and flat print.

204 6.6.3 The outcome of this process is that the printed image can display the following 

205 characteristics:

206 6.6.3.1 Raised print, flat print, or a combination of both.

207 6.6.3.2 Under magnification, there is a very fine dot like appearance and a grid pattern may 

208 be visible.

209 6.6.3.3 Currently the process is only used to produce monochrome prints and not color

210 images for identity documents.

211 6.6.3.4 Can produce a moiré (e.g. having a rippled, lustrous finish) affect depending on the 

212 type of substrate.
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213

214 FIG. 8 Example of a Laser Engraved print

215 (Full facial image printed at 380 DPI and scanned at 1200 DPI for this guideline)

216
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217 7. Recommendations

218 In the image analysis phase (which is done before the actual comparison is started), it is best 

219 practice for the facial examiner to determine whether the image referred for facial comparison is 

220 a digital live capture image or a capture of a printed facial image. The reference images for the 

221 common printing processes in this document demonstrate that magnification of the printed image 

222 may not assist in a detailed morphological comparison of the facial component features. 

223 The determination that the image is from a printed product will assist in identifying potential 

224 limitations that may affect the suitability of the image or the ability of the facial examiner to 

225 conduct a full morphological image comparison. The effects of the printing processes outlined in 

226 this guideline and the resolution of the captured image may limit the facial examiner to a holistic 

227 image comparison.

228 Of the six common printing processes described in this guideline:

229 • Conventional and Digital Photographic and Dye Sublimation printing processes are more 

230 likely to provide an image suitable for a detailed facial morphological comparison. 

231 • The Laser Engraving printing process will be the least likely to provide an image suitable 

232 for a detailed facial morphological comparison.

233

234
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235 Appendix

236 Image Resolution in this Guideline

237 All images provided within this document are to illustrate the basic concepts of printing 

238 processes. To demonstrate each of the printing processes covered in this guideline, the following 

239 two types of images contained within the guideline have been scanned at a high-resolution of 

240 1200 DPI:

241 • A full facial image.

242 • A magnified view of the eye area to illustrate a close-up view of the characteristics and 

243 effects of each printing process.

244 The original image capture resolution for the full facial image was 300 PPI and has not been 

245 changed except for automated image processing during personalization of sample images to 

246 demonstrate each of the printing processes.

247 The resolution or PPI settings of the facial image for printing can dictate the quality of the 

248 image output. Photographic prints are usually at 300 DPI. For identity documents, the print 

249 resolution for a facial image can vary from 96 DPI up to 1200 DPI. 

250 Facial images in identity documents typically have a print size of 35-40mm wide and 45-

251 50mm high. Consequently, these dimensions have been used to produce the printed facial images 

252 in this guide.