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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

OSAC 2022-S-0001

Standard Guide for Image 

Comparison 

Conclusions/Opinions

Facial Identification Subcommittee

Digital/Multimedia Scientific Area Committee

Organization of Scientific Area Committees (OSAC) for Forensic Science
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

DraftOSAC Proposed Standard

OSAC 2022-S-0001

Standard Guide for Image 

Comparison Conclusions/Opinions

Prepared by

Facial Identification Subcommittee

Version: 1.0

September 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.

To be placed on the OSAC Registry, certain types of standards first must be reviewed by a Scientific and 

Technical Review Panel (STRP). The STRP process is vital to OSAC’s mission of generating and 

recognizing scientifically sound standards for producing and interpreting forensic science results. The 

STRP shall provide critical and knowledgeable reviews of draft standards or of proposed revisions of 

standards previously published by standards developing organizations (SDOs) to ensure that the 

published methods that practitioners employ are scientifically valid, and the resulting claims are 

trustworthy.

The STRP panel will consist of an independent and diverse panel, including subject matter experts, 

human factors scientists, quality assurance personnel, and legal experts, which will be tasked with 

evaluating the proposed standard based on a comprehensive list of science-based criteria.

For more information about this important process, please visit our website 

at: https://www.nist.gov/topics/organization-scientific-area-committees-forensic-science/scientifictechnical-review-panels. 
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

Standard Guide for Image Comparison Conclusions/Opinions1 1

2

3

4 1. Scope

5 1.1 This standard defines conclusions (hereafter “opinions”) categories that shall be reached 

6 by a practitioner performing comparisons of people, objects, or scenes captured in images (e.g., 

7 face, vehicle, clothing, skin detail, etc.), regardless of the process by which opinions are reached 

8 (i.e., the examination methodology).

9 1.1.1 This standard does not address opinions stated in terms of quantitative probability 

10 models, to include numerical assessments of the strength or weight of evidence, or the 

11 documentation or reporting of opinion (FISWG Minimum Guidelines for Facial Image 

12 Comparison Documentation, SWGDE Technical Overview for Forensic Image Comparison). 

13 1.1.2 This standard does not supersede published opinion scale standards for other 

14 disciplines.

15 1.2 This standard does not purport to address all of the safety concerns, if any, associated 

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

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

18 1.3 This standard is intended to be used by individuals with discipline specific knowledge, 

19 skills, and abilities acquired through education, training, and experience. 

20

21 2. Referenced Documents

1 There is a movement in the forensic community to eliminate the word “conclusion” from the formal set of words that describe forensic processes. 

For example, ISO does not use the word “conclusion”. This is reflected by the Organization of Scientific Area Committees for Forensic Science (OSAC) 

preference to use the term “opinion” (defined as View, judgment, belief – takes into consideration other information in addition to observations, data, 

calculations, and interpretations).
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

22 2.1 ASTM Standards: 

23 2.1.1 Standard Guide for Facial Image Comparison Feature List for Morphological Analysis 

24 (E3149)

25 2.2 FISWG Standards: 

26 2.2.1 FISWG Minimum Guidelines for Facial Image Comparison Documentation

27 2.3 SWGDE Standards:

28 2.3.1 SWGDE Best Practices for Photographic Comparison for All Disciplines

29 2.3.2 SWGDE Technical Overview for Forensic Image Comparison

30

31 3. Terminology

32 3.1 Definitions specific to this standard:

33 3.1.1 source, n—the person, object, or scene captured in the images being compared 

34 4. Significance and Use

35 4.1 This standard should be used by organizations performing source determination of 

36 people, objects, or scenes depicted in images and lack a quantitative assessment mechanism. 

37 4.2 Any mention of probability within this document refers to a subjective probability based 

38 on the knowledge, skills, and experience of the practitioner. It should be stated when no 

39 empirical studies currently exist for a given type of evidence and interpretation.

40 4.3 To ensure interorganizational consistency, this framework categorizes opinions based on 

41 the level of support the data shows for the propositions under consideration. When defining 

42 opinion scales, organizations shall consider alternative propositions (both the propositions of 

43 same source and of not same source).
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

44 4.4 Individual organizations may label their opinions scales differently, but they should 

45 explicitly correspond to the opinion categories as defined in this standard.

46 4.5 The opinion categories “Support for Exclusion” and “Support for Common Source” may 

47 be expanded to include multiple opinions of more specific levels of confidence based on 

48 organization specific needs. 

49 5. Opinion Categories

50 5.1 Exclusion: an opinion that the observed characteristics do not depict the same source

51 where a minimum of one irreconcilable discrepancy is observed. 

52 5.2 Support for Exclusion: an opinion that the observed dissimilar characteristics outweigh

53 the similar characteristics but are insufficient to reach an exclusion. The observed characteristics 

54 are more probable given the proposition that the images depict different sources, rather than the 

55 proposition that they depict the same source.

56 5.3 Inconclusive: The basis of this opinion is that the observed characteristics are equally

57 probable given the proposition that the images depict different sources and the proposition that 

58 the images depict the same source.

59 5.4 Support for Common Source: an opinion that the observed similar characteristics 

60 outweigh the observed dissimilar characteristics but are insufficient to reach strong support for 

61 common source. The observed characteristics are more probable given the proposition that the 

62 images depict the same source, rather than the proposition that they depict the different sources. 

63 5.5 Strong Support for Common Source: an opinion that the observed similar characteristics 

64 far outweigh the observed dissimilar characteristics. The observed characteristics are much more 
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

65 probable given the proposition that the images depict the same source, rather than the proposition 

66 that they depict the different sources. 

67 5.5.1 A practitioner shall not assert the opinion that two items (e.g., faces, vehicles, 

68 clothing, skin detail, etc.) originated from the same source to the exclusion of all others. A 

69 practitioner shall not use terms in the stated opinion such as “individualize,” “individualization,” 

70 or express an absolute certainty or any numerical value of certainty. Such an assertion would be 

71 scientifically unsupportable and may wrongly imply a common source is based upon a 

72 statistically-derived or verified measurement, or comparison of all features of the object in the 

73 world's population, rather than a practitioner’s opinion.

74
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

APPENDIX2 75

76

77 X1. OBJECT COMPARISON EXAMPLES

2 Examples contributed from OSAC VITAL and Facial Identification Subcommittees
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

78 X1.1 Exclusion 

79 X1.1.1 An image of a 2-door coupe is compared to an image of a 4-door sedan.

80 X1.1.2 Reasoning: The vehicles have irreconcilable observed discrepancies, 2-doors as 

81 opposed to 4-doors.

82 X1.2 Support for Exclusion

83 X1.2.1 Images of two similar colored, make/model and generation (year range of 

84 manufacturing) vehicles (class characteristics) are compared. One of the depicted vehicles has 

85 visible damage with rust on the passenger door.

86 X1.2.2 Reasoning: The damage could have occurred after the one image was captured 

87 making the damage an explainable dissimilarity.

88 X1.3 Inconclusive 

89 X1.3.1 Images of two similar colored, but indeterminate make/model and generation vehicles 

90 are compared.

91 X1.3.2 Reasoning: These are only class characteristics and millions of these vehicles were 

92 manufactured. No observable features that would support exclusion or common source opinions.

93 X1.4 Support for Common Source

94 X1.4.1 Images of two similar colored, make/model and generation vehicles with damage in 

95 the same location and of comparable shape and size are compared.

96 X1.4.2 Reasoning: Observed feature (similar damage) would support that the vehicles could 

97 be the same.

98 X1.5 Strong Support for Common Source

99 X1.5.1 Images of two similar colored, make/model and generation vehicles with multiple 

100 points of damage in the same locations and of comparable shapes and sizes, are compared.
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

101 X1.5.2 Reasoning: Observed features, including the shapes, sizes and positional relationship 

102 to each other, supports that the vehicles are same more than any other opinion.

103

104 X2. FACE COMPARISON EXAMPLES

105 For all examples in this section, the following assumptions must be considered: reason for the 

106 comparison--individuals look similar, identical capture conditions and image quality

107 X1.6 Exclusion 

108 X1.6.1 An image depicting an elderly individual with a long face and narrow-set eyes 

109 compared to an image depicting a young individual with a round face and wide-set eyes (the 

110 images are captured contemporaneously).

111 X1.6.2 Reasoning: The subjects show irreconcilable differences in that the face shape and 

112 eye-set are skeletally determined and are not easily changed.

113 X1.7 Support for Exclusion

114 X1.7.1 An image depicting a young individual with a round face and wide set eyes compared 

115 to an image depicting a young individual with a round face, wide-set eyes, and an apparent scar 

116 on the right cheek (timing of images is unknown).

117 X1.7.2 Reasoning: The scar on the right cheek could be an explainable or unexplainable 

118 dissimilarity, depending on the timing of the images.

119 X1.8 Inconclusive

120 X1.8.1 An image depicting a young individual with a round face and wide-set eyes with a 

121 scar on the right cheek compared with an image depicting a young individual with a round face 

122 and wide-set eyes wearing a surgical mask that precludes observations of the presence or absence 
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OSAC 2022-S-0001 Standard Guide for Image Comparison 

Conclusions/Opinions

123 of a scar and other potentially comparable characteristics of the lower face (the images are 

124 captured contemporaneously).

125 X1.8.2 Reasoning: Insufficient observable features that would support exclusion or common 

126 source opinions.

127 X1.9 Support for Common Source

128 X1.9.1 An image depicting a young individual with a round face and wide set eyes compared 

129 to an image depicting a young individual with a round face, wide-set eyes, and an apparent scar 

130 on the right cheek (the latter image was captured years after the former).

131 X1.9.2 Reasoning: Facial components, characteristics, and characteristic descriptors suggest 

132 that the subjects could be the same and observed differences are explainable.

133 X1.10 Strong Support for Common Source

134 X1.10.1 An image depicting a young individual with a round face, wide-set eyes, and a scar 

135 on the right cheek compared to an image depicting a young individual with a round face, wide136 set eyes, and a scar of the same dimensions, orientation, and color on the right cheek (the images 

137 are captured contemporaneously).

138 X1.10.2 Reasoning: Facial components, characteristics, and characteristic descriptors suggest 

139 that the subjects could be the same and observed differences are explainable. This category 

140 would be differentiated from Support for Common Source based on the discriminating power of 

141 the observed facial components, characteristics, and characteristic descriptors.

142