OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Standard for Feature 

Selection in Friction Ridge 

Examination

Friction Ridge Subcommittee

Physics/Pattern Interpretation Scientific Area Committee

Organization of Scientific Area Committees (OSAC) for Forensic Science
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Draft OSAC Proposed Standard

Standard for Feature Selection in 

Friction Ridge Examination

Prepared by 

Friction Ridge Subcommittee

Organization for Scientific Area Committees (OSAC) for Forensic Science

Version: 1.0

September 2022

Disclaimer:

This OSAC Proposed Standard was written by 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. 
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

1 Table of Contents

2 1. Introduction ..................................................................................................................... 2

3 2. Scope ................................................................................................................................. 2

4 3. Terms and Definitions..................................................................................................... 2

5 4. General Requirements .................................................................................................... 3

6 5. General Recommendations........................................................................................... 13

7 6. Appendix A: Edge Shapes............................................................................................. 21

8 7. Appendix B: Minutiae................................................................................................... 22

9 8. Appendix C: Incipient Ridges and Dissociated Ridges.............................................. 25

10 9. Appendix D: Pattern Elements..................................................................................... 27

11 10. Appendix E: Ridge Flows ............................................................................................. 32

12 11. Appendix F: Regular and Irregular Creases of the Hands and Feet........................ 34

13 12. Appendix G: Wrinkles.................................................................................................. 37

14 13. Appendix H: Scars......................................................................................................... 38

15 14. Appendix I: Unstable Features..................................................................................... 39

16 15. Appendix J: Relationship of Features ......................................................................... 41

17 16. Appendix K: Quick Reference Summary Table......................................................... 44

18 17. Appendix L: References................................................................................................ 48

19 18. Appendix M: Change Log............................................................................................. 49

20

21
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

22 1. Introduction

23 1.1. This standard has been developed with the objective of improving the quality and 

24 consistency of friction ridge examination practices. 

25

26 1.2. This standard provides a comprehensive list of features and their definitions which can be 

27 used during the friction ridge examination process. 

28

29 1.3. In addition to the standardized list of features and their definitions, this standard also 

30 includes information about the diagnosticity of those features. The diagnostic value of 

31 each feature is expanded upon where applicable, by recognizing shared features within a

32 population and rarity features in the population. This information is based on the consensus 

33 opinion of the OSAC Friction Ridge Subcommittee where supporting evidence in the 

34 scientific literature is limited.

35

36 1.4. In addition to the significance of each feature, this standard provides an awareness of the 

37 relationship between features that can be used during examination.

38

39 1.5. In this standard, the following verbal forms are used: “shall” indicates a requirement, 

40 “should” indicates a recommendation; “may” indicates permission; and “can” indicates a 

41 possibility or capability.

42

43 2. Scope

44 2.1. This standard specifies the features that can be utilized during friction ridge 

45 examinations.

46

47 2.2. This standard does not address the examination methodology or documentation.

48

49 3. Terms and Definitions

50 For the purposes of this document, the following terms and definitions apply.

51

52 3.1. Examination: The act or process of observing, searching, detecting, recording, 

53 prioritizing, collecting, analyzing, measuring, comparing, and/or interpreting.

54

55 3.2. Examiner (Friction Ridge)/Competent Friction Ridge Examiner: An individual who has 

56 successfully completed their FSP’s training program and has demonstrated to the FSP 

57 that they possess the knowledge, skills and abilities to perform the tasks required of their 

58 current position. An individual authorized to conduct friction ridge examinations for the 

59 FSP by observing and interpreting data, making decisions, forming conclusions and 

60 opinions, issuing reports and/or providing testimony.

61
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62 3.3. Pattern force area: A region of friction ridge skin in which minutiae of a particular type 

63 are forced to form due to the flow of the ridges. 

64

65 3.4. Rarity (of a feature type): The frequency of which a type of feature is encountered in a 

66 group of people (its prevalence), either in isolation or in conjunction with other 

67 information about its local context. 

68

69 3.5. Source: an individual from which an item (e.g., crime scene impression) originates.

70

71 4. General Requirements

72 4.1. The following feature list contains friction ridge features and their associated attributes 

73 that examiners may use during examination of friction ridge impressions.

74

75 4.2. Only those features included on this list shall be considered during friction ridge 

76 examinations to support suitability determinations and source conclusions.

77

78 4.3. The features that can be used during friction ridge examinations include the following:

79

80 4.3.1. Ridges: 

81

82 The ridges are the core feature type in the friction ridge skin. The ridges are the 

83 fully formed papillary lines on the volar surfaces of normal human hands and feet. 

84 On the skin, fully formed ridges can be distinguished from incipient ridges by the 

85 existence of sweat pores spaced somewhat evenly along the path of the ridge. If 

86 the friction ridge skin is considered a topographical map, the ridges are typically 

87 the feature at the highest elevation and are the main contact regions when the 

88 friction ridge skin touches a surface. The combination of ridge morphology and 

89 pores often impart a distinctive texture within a region of skin or within an 

90 impression. See Appendix A for definitions and examples of morphology edge 

91 shapes.

92

93 4.3.1.1. Attributes:

94

95 4.3.1.1.1. Number – count of ridges. 

96

97 4.3.1.1.2. Ridge Width – distance between the sides of a ridge at a given 

98 location on the ridge.

99

100 4.3.1.1.3. Furrow Width – distance between the sides of adjacent ridges at a 

101 given location on the ridges.

102

103 4.3.1.1.4. Length – distance between two locations along the path of a ridge.

104

105 4.3.1.1.5. Spacing – distance between the midpoints of two adjacent ridges.
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106

107 4.3.1.1.6. Direction – direction of the path of a ridge in relation to a fixed 

108 point in the skin or impression (e.g., a ridge that is perpendicular to 

109 an irregular crease).

110

111 4.3.1.1.7. Curvature – change in angles along the path of a ridge for a given 

112 segment of the ridge.

113

114 4.3.1.1.8. Edge Shape – contour of the edge of a ridge (straight, protrusion, 

115 and intrusion).

116

117 4.3.1.1.9. Pore Position – location of a pore with respect to the edge of the 

118 ridge or another pore.

119

120 4.3.1.1.10. Open Field – minimum of four ridges in sequence with a visible 

121 length of at least 3mm each where no minutiae are present.

122

123 4.3.2. Minutiae: 

124

125 A minutia defines the end of a ridge. A ridge can end in three different manners: 

126 1) no connection to the adjacent ridge above the level of the furrow (i.e., ending 

127 ridge), 2) completely connected to the adjacent ridge from the bottom of the 

128 furrow to the top of the ridge (i.e., bifurcation) or 3) partially connected to the 

129 adjacent ridge (i.e., ambiguous minutiae).

130

131 4.3.2.1. Attributes:

132

133 4.3.2.1.1. Number – count of minutiae within a region of skin or within an 

134 impression of the skin.

135

136 4.3.2.1.2. Density – number of minutiae within a specified surface area (e.g., 

137 high or low or per mm2).

138

139 4.3.2.1.3. Direction – angle of the path of the ridge emanating from the 

140 minutia in relation to a fixed point in the skin or impression.

141

142 4.3.2.1.4. Connectedness – extent to which the end point of one ridge is 

143 connected to a neighboring ridge.

144

145 4.3.2.1.5. Compound Minutiae – the atypical combination of multiple 

146 minutiae within a close proximity or that manifest as a single 

147 structure. Compound minutiae may include the following: short 

148 ridge, dot, break, enclosure, overlap, crossbar, bridge, spur, ending 

149 ridge and bifurcation combination, opposing bifurcations, dock, 

150 trifurcation, return, and merge point. See Appendix B for 

151 definitions and examples of simple and compound minutiae.
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152

153 4.3.3. Incipient Ridges: 

154

155 Incipient ridges are raised papillary ridges that are typically lower in elevation 

156 than the mature ridges (Section 4.3.1). Incipient ridges occupy space in the 

157 furrows, between the main ridges. Unlike the main ridges, incipient ridges do not 

158 have sweat pores. Incipient ridges are typically less than one half the average 

159 width of the surrounding ridges and often display numerous breaks. See Appendix 

160 C for examples of incipient ridges.

161

162 4.3.3.1. Attributes:

163

164 4.3.3.1.1. Number – count of incipient ridges within a region of skin or 

165 within an impression of the skin.

166

167 4.3.3.1.2. Density – number of incipient ridges within a specified surface 

168 area (e.g., high or low or per mm2).

169

170 4.3.3.1.3. Length – distance between two locations along the path of an 

171 incipient ridge.

172

173 4.3.3.1.4. Direction – direction of the path of an incipient ridge in relation to 

174 a fixed point in the skin or impression (e.g., an incipient ridge that 

175 is perpendicular to an irregular crease).

176

177 4.3.3.1.5. Inter-Incipient Break – distance between the ends of two incipient 

178 ridges (i.e., the gap between incipient ridges within a row of 

179 incipient ridges).

180

181 4.3.3.1.6. Edge Shapes – contours along the edges of an incipient ridge 

182 (straight, protrusion, and intrusion).

183

184 4.3.4. Dissociated Ridges: 

185

186 Dissociated ridges are raised portions of the friction ridge skin that are broken 

187 into short, wavy or dotlike segments that may be completely disorganized or 

188 somewhat follow the ridge flow in a given region of skin. Dissociated ridges are 

189 typically at the same elevation as any surrounding normal ridges and may or may 

190 not contain sweat pores. Dissociated ridges are also known as dysplasia. See 

191 Appendix C for examples of dissociated ridges.

192

193 4.3.4.1. Attributes:

194

195 4.3.4.1.1. Number – count of ridge segments within a region of skin or 

196 within an impression of the skin.

197
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198 4.3.4.1.2. Density – number of ridge segments within a specified surface area 

199 (e.g., high or low or per mm2).

200

201 4.3.4.1.3. Ridge Width – distance between the sides of a ridge segment at a 

202 given location on the segment.

203

204 4.3.4.1.4. Furrow Width – distance between the sides of adjacent ridges at a 

205 given location on the ridges.

206

207 4.3.4.1.5. Length – distance between two locations along the path of a ridge 

208 segment.

209

210 4.3.4.1.6. Spacing – distance between the midpoints of two adjacent ridges.

211

212 4.3.4.1.7. Direction – direction of the segment of a ridge in relation to a fixed 

213 point in the skin or impression (e.g., a segment that is 

214 perpendicular to the core of a loop).

215

216 4.3.4.1.8. Curvature – change in angles along the path of a ridge segment.

217

218 4.3.4.1.9. Edge Shape – contour of the edge of a ridge segment (straight, 

219 protrusion, indentation, and discontinuity).

220

221 4.3.4.1.10. Pore Position – location of a pore with respect to the edge of the 

222 ridge segment or another pore.

223

224 4.3.4.1.11. Connectedness – extent to which the end point of one ridge 

225 segment is joined or linked to a neighboring ridge (ridge ending, 

226 bifurcation, ambiguous).

227

228 4.3.5. Ridge flow: 

229

230 Ridge flows are uninterrupted courses of ridges commonly found in specific regions 

231 of the hands and feet that reflect the stresses on the surface of the skin caused by 

232 the growth of the hands and feet and the presence of the regular flexion creases at 

233 the time the ridges are forming. These ridge flows are not defined “pattern

234 elements,” but useful during the examination process because they are predictive 

235 for each region of the hand and foot. See Appendix E for examples of ridge flows 

236 and attributes.

237 In this standard, ridge flows include the fingerprint pattern traditionally classified 

238 as a plain arch. The inclusion of the plain arch as a ridge flow rather than a pattern 

239 is because the plain arch is the result of the complete or near-complete regression 

240 of the volar pad during embryological development of the skin. The lack of a 

241 volar pad permits the general growth stresses to be the primary influence on the 

242 ridge flow, causing the ridges to simply flow from one side of the finger to the 
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

243 other, similar to the lower portions of the fingers and other regions of the palms 

244 and soles. The distinction between “pattern elements” and “ridge flow” in this 

245 standard is not intended to preclude the use of the plain arch to describe the ridge 

246 flow in the fingers or toes.

247

248 4.3.5.1. Attributes:

249

250 4.3.5.1.1. Curvature – change in angle along a series of parallel ridges at a 

251 given location along a ridge flow.

252

253 4.3.5.1.2. Convergence – loss of ridges along a ridge flow, causing an overall 

254 decrease in the width of the ridge flow.

255

256 4.3.5.1.3. Divergence – gain of ridges along a ridge flow, causing an overall 

257 increase in the width of the ridge flow.

258

259 4.3.6. Pattern Elements – Recurves and Triradii: 

260

261 The term “pattern” is most often associated with the rules for classifying the 

262 patterns in the distal segments of the fingers. Fingerprint classification rules are 

263 inadequate when seeking a comprehensive description of the patterns across the 

264 hands and feet. For instance, the pattern in the distal portion of the finger is 

265 classified as an arch when the ridges flow transversely and lack a core or triradius. 

266 The proximal and medial portions of the fingers are not described as having an 

267 “arch” pattern, despite the ridges flowing transversely and lacking a triradius and 

268 core.

269

270 For this document, ridge flow will refer to the main course of a group of ridges as 

271 dictated by the general growth stresses on the friction ridge skin caused by the 

272 growth of the hand or foot and the presence of regular flexion creases during the 

273 embryological development of the skin. Pattern elements will be considered any 

274 deviation from the general ridge flow as a result of the influence of the volar pads 

275 during embryological development. For this reason, a triradius (commonly 

276 referred to as a “delta” in fingerprint classification), will be considered its own 

277 pattern element and plain arches will be described under Ridge Flow (Section 

278 4.3.5). This distinction permits a unified approach to the entire friction ridge skin 

279 and the expansion of relationships between two pattern elements and between a 

280 pattern element and other features. See Appendix D for definitions and examples 

281 of the patterns as described in this standard. Depending on the pattern element, 

282 different attributes can be considered.

283

284 4.3.6.1. Attributes:

285

286 4.3.6.1.1. Number – count of recurves and triradii within a region of the 

287 friction ridge skin or in an impression. NOTE: For the purposes of 

288 this document, a whorl is considered a continuous recurve.
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289

290 4.3.6.1.2. Triradius Angle – angle formed by two rays of a triradius.

291

292 4.3.6.1.3. Core Ridge Count – number of ridges enclosed by a recurving 

293 ridge in a tented arch, loop, or whorl; number of ridges enclosed by 

294 the two triradii of a column; number of perpendicular ridges that 

295 form a vestige.

296

297 4.3.6.1.4. Core Length – distance from the geometric center of a triradius to 

298 the innermost recurve surrounding the ray of the triradius in a 

299 tented arch. The distance between opposing innermost recurves of 

300 a whorl.

301

302 4.3.6.1.5. Pattern Element Relationships – ridge counts, distance, or angles 

303 between the cores, recurves, or triradius centers of two or more 

304 pattern elements.

305

306 4.3.7. Regular Creases: 

307

308 The regular creases are those flexion creases which form prior to the friction ridges 

309 and prior to flexion of the hand or foot during embryological formation. Regular 

310 creases are tightly bound to the underlying palmar aponeurosis and ridges tend not 

311 to traverse through these creases. Regular creases are also referred to as primary 

312 creases or major creases. The five regular creases of the palm include: wrist crease, 

313 thenar crease, distal transverse crease, proximal transverse crease, and palmar 

314 digital creases. The only regular creases associated with the sole are the plantar 

315 digital flexion creases where the skin of the toe meets the sole. 

316 Thumbs and great toes typically have a distal interphalangeal crease located at the 

317 joint between the distal and proximal phalanges (there is typically no medial 

318 phalange in the great toe or thumb). The four remaining digits of the hands and 

319 feet typically have a distal interphalangeal crease located at the joint of the distal 

320 and medial phalanges. The four fingers of the hand typically have a proximal 

321 interphalangeal crease located at the joint of the medial and proximal phalanges. 

322 In the remaining four toes, it is common for the proximal interphalangeal crease 

323 to be poorly formed or missing. See Appendix F for a schematic of the regular 

324 creases of the hands and feet.

325

326 4.3.7.1. Attributes:

327

328 4.3.7.1.1. Number – count of regular creases within a region of skin or within 

329 an impression of a skin.

330

331 4.3.7.1.2. Configuration – organization of the regular crease as a single 

332 structure or a double structure (e.g., the palmar digital crease of the 
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333 middle finger is typically a double crease while the palmar digital 

334 crease of the index finger is typically a single crease).

335

336 4.3.7.1.3. Spacing – distance between the midpoints of two adjacent creases.

337

338 4.3.7.1.4. Position – location of a regular crease within the structure of the 

339 hand or foot.

340

341 4.3.7.1.5. Width – distance between the sides of a regular crease at a given 

342 location on the regular crease.

343

344 4.3.7.1.6. Length – distance between two locations along the path of a 

345 regular crease.

346

347 4.3.7.1.7. Curvature – change in angle along the path of a regular crease for a 

348 given segment of the crease.

349

350 4.3.7.1.8. Direction – path of a regular crease in relation to a fixed point in 

351 the skin or impression (e.g., a crease that is parallel to the direction 

352 of the surrounding ridges).

353

354 4.3.7.1.9. Edge shapes – contours of the skin contained within a regular 

355 crease.

356

357 4.3.7.1.10. Branching – pattern of branching along the main line of a regular 

358 crease.

359

360 4.3.8. Irregular Creases: 

361

362 The irregular creases are those flexion creases which form during or after ridge 

363 formation (ridges typically traverse through these creases). Although not as deep 

364 as the regular creases, the irregular creases also have attachments to the 

365 underlying structure of the hand or foot. The irregular creases show greater 

366 variability than the regular creases within the human population. See Appendix F 

367 for examples of irregular flexion creases.

368

369 4.3.8.1. Attributes:

370

371 4.3.8.1.1. Number – count of irregular creases within a region of skin or 

372 within an impression of a skin.

373

374 4.3.8.1.2. Density – number of irregular creases within a specified surface 

375 area (e.g., high or low or per mm2).

376

377 4.3.8.1.3. Width – distance between the sides of an irregular crease at a given 

378 location on the irregular crease.
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379

380 4.3.8.1.4. Length – distance between two locations along the path of an 

381 irregular crease.

382

383 4.3.8.1.5. Curvature – change in angle along the path of an irregular crease 

384 for a given segment of the crease.

385

386 4.3.8.1.6. Direction – the path of an irregular crease in relation to a fixed 

387 point in the skin or impression (e.g., a crease that is parallel to the 

388 direction of the surrounding ridges).

389

390 4.3.8.1.7. Branching – branching pattern along the main line of an irregular 

391 crease.

392

393 4.3.8.1.8. Angle of intersection – angle(s) created by the intersection of two 

394 or more irregular creases.

395

396 4.3.8.1.9. Spacing – distance between the midpoints of two adjacent creases.

397

398 4.3.9. Wrinkles: 

399

400 Wrinkles are a result of a breakdown in the skin over time. The disorganization of 

401 the various fibers and large proteins in the dermis causes the dermis to fold 

402 inward, causing a crimp in the epidermis. Unlike the regular and irregular creases, 

403 wrinkles do not have dedicated attachments to the underlying structure of the 

404 hand or foot. See Appendix G for examples of wrinkles.

405

406 4.3.9.1. Attributes:

407

408 4.3.9.1.1. Number – count of wrinkles within a region of skin or within an 

409 impression of a skin.

410

411 4.3.9.1.2. Density – number of wrinkles within a specified surface area (e.g., 

412 high or low or per mm2).

413

414 4.3.9.1.3. Width – distance between the sides of a wrinkle at a given location 

415 on the wrinkle.

416

417 4.3.9.1.4. Length – distance between two locations along the path of a 

418 wrinkle.

419

420 4.3.9.1.5. Curvature – the curvature of a wrinkle at a given location.

421

422 4.3.9.1.6. Direction – the path of a wrinkle in relation to a fixed point in the 

423 skin or impression (e.g., a wrinkle that is parallel to the direction of 

424 the surrounding ridges).
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425

426 4.3.9.1.7. Branching – branching pattern along the main line of a wrinkle.

427

428 4.3.9.1.8. Angles of intersection – angle(s) created by the intersection of two 

429 or more wrinkles.

430

431 4.3.9.1.9. Spacing – distance between the midpoints of two adjacent 

432 wrinkles.

433

434 4.3.10. Scars: 

435

436 A scar is a disfiguration of the skin as a result of wound healing. The disfiguration 

437 can occur in varying degrees dependent on the amount of skin contraction 

438 experienced at the site of the injury and medical intervention (e.g., stitches). Some 

439 scars are imperceptible, while others are dramatic. Additionally, scars initiated by 

440 temperature and chemical burns tend to disfigure the skin differently than cuts or 

441 punctures. Simple, linear scars tend to exist at a lower elevation than the tops of 

442 the ridges. Complex scars and scars that contain epithelial islands can exist at the 

443 same or higher elevation than the normal ridges. See Appendix H for examples of 

444 scars.

445

446 4.3.10.1. Attributes:

447

448 4.3.10.1.1. Number – count of scars within a region of skin or within an 

449 impression of a skin.

450

451 4.3.10.1.2. Width – distance between the sides of a scar at a given location on 

452 the scar.

453

454 4.3.10.1.3. Length – distance between two locations along the path of a scar.

455

456 4.3.10.1.4. Surface Area – measure of a total area of the surface the scar 

457 occupies.

458

459 4.3.10.1.5. Curvature – change in angle along the path of a scar for a given 

460 segment of a scar.

461

462 4.3.10.1.6. Direction – path of a scar in relation to a fixed point in the skin or 

463 impression (e.g., a scar that is perpendicular to the direction of the 

464 surrounding ridges).

465

466 4.3.10.1.7. Created Minutiae – new minutiae created at the border of a scar 

467 due to the misalignment of the original ridges during the healing 

468 process.

469
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470 4.3.10.1.8. Edge Shapes – contours defined by the border of a scar and any 

471 epithelial islands created as a result of the injury.

472

473 4.3.11. Unstable features: 

474

475 Unstable features are those features temporarily present in the skin as the result of 

476 wound healing or disease. Unstable features include, but are not limited to, warts, 

477 eczema/psoriasis, actively healing injuries, calluses, and blisters. Depending on 

478 the nature of the unstable feature, it may exist lower, equal, or higher elevations 

479 than the tops of the main ridges. See Appendix I for examples of more common 

480 unstable features found in the friction ridge skin.

481

482 4.3.11.1. Attributes:

483

484 4.3.11.1.1. Number – count of unstable features within a region in the skin or 

485 impression.

486

487 4.3.11.1.2. Width – distance between the sides of unstable feature at a given 

488 location on the unstable feature.

489

490 4.3.11.1.3. Length – distance between two locations along the path of an 

491 unstable feature.

492

493 4.3.11.1.4. Surface Area – measure of a total area of the surface the unstable 

494 feature occupies.

495

496 4.3.11.1.5. Curvature – change in angle along the path of an unstable feature 

497 for a given segment of the feature.

498

499 4.3.11.1.6. Direction – path of an unstable feature in relation to a fixed point 

500 (e.g., scrape that is parallel to the direction of the surrounding 

501 ridges).

502

503 4.3.11.1.7. Branching – branching pattern along the main line of an unstable 

504 feature.

505

506 4.3.11.1.8. Edge Shapes – contours of an unstable feature.

507

508 4.3.12. Shape of the Impression: 

509

510 The surface area and border contours of a friction ridge impression.

511

512 4.3.12.1. Attributes:

513

514 4.3.12.1.1. Surface Area – measure of a total area of the surface the 

515 impression (e.g., size).
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516

517 4.3.12.1.2. Outline – the contours along the border of the impression.

518

519 5. General Recommendations

520 5.1. Distortion factors affecting the appearance of features should be considered when 

521 conducting friction ridge examinations. Distortion factors of friction ridge features are

522 considered from two perspectives: biological and recordability. 

523

524 5.1.1. Biological distortion factors are those factors that affect the expected stability of 

525 the feature in the friction ridge skin. 

526

527 5.1.2. Recordability distortion factors are those factors that can affect the appearance of 

528 the features when they are recorded in an impression. 

529

530 5.2. The following distortion factors are not meant to be exhaustive of all possibilities, but 

531 reflective of common causes for features to appear different over time or due to 

532 circumstances of touch. The following definitions are meant to provide common 

533 language to describe distortion factors and provide a list of topics that would benefit 

534 from additional research.

535

536 5.2.1. Adolescent growth – growth of the hand or foot from the time the ridges form until 

537 adult size is attained (typically late teens).

538

539 5.2.2. Aging – changes in the friction ridge skin that take place because of the natural 

540 aging process; typically, these changes begin after the age of forty.

541

542 5.2.3. Injury – physical damage to the hand, foot, or friction ridge skin that elicits a wound 

543 healing response (e.g., cut or burn); certain injuries can result in the formation of a 

544 scar.

545

546 5.2.4. Disease – disorder in the structure or function of the skin that produces specific 

547 signs or symptoms and is not related to a physical injury (e.g., wart, psoriasis, or 

548 acquired ridge aplasia).

549

550 5.2.5. Hand flexion – the bending of the digits at the joints or the rotation of the thumb.

551

552 5.2.6. Abduction of digits – the degree to which the digits are spread apart from one 

553 another.

554

555 5.2.7. Angle of contact – the position of the hand or foot with respect to the surface during 

556 contact.

557

558 5.2.8. Compressive stress – the squeeze of the skin between the boney portions of the 

559 hand or foot and a surface (also referred to as “deposition pressure”).
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

560

561 5.2.9. Shearing stress – tangential force applied to the skin (also referred to as “lateral 

562 pressure”).

563

564 5.2.10. Torque – rotational force applied to the skin.

565

566 5.2.11. Residue factors – any factors related to the residue on the skin that can affect the 

567 recording of the skin (e.g., initial composition of the residue, distribution of residue 

568 on the skin, or redistribution of residue in an impression due to skin moving on a 

569 surface).

570

571 5.2.12. Surface conditions – any factors related to the surface that affect the recording of 

572 the skin (e.g., texture, curvature, pliability, or contaminants).

573

574 5.2.13. Environmental factors – any factors related to the environment (e.g., temperature, 

575 humidity, UV exposure, or time) that affect the appearance of the features after the 

576 impression is recorded on a surface.

577

578 5.2.14. Post-deposition factors – any non-environmental factors that affect an impression 

579 (e.g., overlays with other impressions or smearing caused by an object touching an 

580 impression).

581

582 5.2.15. Processing technique – method used to develop the features of a latent impression; 

583 each method has a signature appearance that can vary, typically because of residue 

584 issues or surface conditions.

585

586 5.2.16. Recovery method – manner in which an impression is preserved (e.g., lift or 

587 photograph) that causes distortion (e.g., crease in tape, lens distortion, poor lighting, 

588 poor focus, low resolution).

589

590 5.2.17. Electronic capture error – inaccurate recording of a feature by an automated device 

591 (e.g., livescan stitching error).

592

593 5.2.18. Atypical anatomy – any deviation from the typical range of shape, size, or 

594 proportions of the human hand or foot or any disruption in the formation of the 

595 skin driven by genetic or epigenetic factors (e.g., syndactyly or congenital ridge 

596 aplasia). Atypical anatomy does not cause issues related to biological stability or 

597 recordability of the features; however, if it is not recognized during analysis, it 

598 can cause an examiner to underestimate or overestimate the source diagnosticity 

599 or search diagnosticity of a given feature set.

600

601 5.3. The diagnosticity of features should be considered when conducting friction ridge 

602 examinations. Diagnosticity, generally, refers to the usefulness of information to assist 

603 in a choice or decision. Diagnosticity of friction ridge features refers to the usefulness of 
OSAC 2022-S-0038 Standard for Feature Selection

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the feature, or attribute of a feature, for establishing search parameters1 604 or the usefulness 

of the feature for determining source2 605 .

606

607 5.4. Features that exhibit low levels of variation in the population should be used for 

608 establishing search parameters. Features with generally low variation include the 

609 following: shape of the impression, creases, pattern elements, and ridge flows. Appendix 

610 J contains examples of how these features can be used to establish search parameters. 

611 Conversely, those features that exhibit higher levels of variation in the human population 

612 are useful for distinguishing one finger, palm, toe, or foot from another. 

613

614 5.5. Pattern elements, ridge flows, and creases can be useful for excluding a given donor, 

615 however these features do not typically provide strong support for same source opinions. 

616

617 5.6. Features that exhibit higher levels of variation in the population should be used to 

618 support same source opinions. The most variable features in the population typically 

619 include the following: ridges, minutiae, incipient ridges, dissociated ridges, and certain 

620 attributes of creases. Acquired features (wrinkles, scars, unstable features) exhibit more 

621 complex diagnosticity, depending on the feature. 

622

623 5.7. The totality (number and diversity) of a specific set of features and available feature 

624 attributes ultimately determines the overall search diagnosticity and source diagnosticity 

625 for a given impression. While most formal research has focused solely on the source 

626 diagnosticity of combinations of minutiae, the remaining features and their attributes add 

627 considerable weight to the various decisions examiners make during the examination 

628 process.

629

630 5.8. The diagnosticity for each of the features include the following:

631

632 5.8.1. Ridges: 

633

634 5.8.1.1. Search Diagnosticity:

635

636 5.8.1.1.1. The search diagnosticity for the ridges is generally low because all 

637 regions of the friction ridge skin are expected to have ridges.

638

639 5.8.1.2. Source Diagnosticity:

640

641 5.8.1.2.1. In general, as the surface area of an impression increases (ergo an 

642 increase in the number of ridges and the visible lengths of the 

643 ridges), the source diagnosticity of the impression also increases.

644

1 Diagnosticity for search parameters refers to the usefulness of the feature to limit the comparisons to specific anatomical regions within the 

hands or feet, left or right hands or feet, or specific orientations. Diagnosticity for search parameters is referred to as “search diagnosticity” in this 

document.

2 Diagnosticity for source determinations refers to the usefulness of the feature to include or exclude a potential donor. Diagnosticity for source 

determinations is referred to as “source diagnosticity” in this document.
OSAC 2022-S-0038 Standard for Feature Selection

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645 5.8.1.2.2. In general, as an open field increases in size (more ridges or longer 

646 visible lengths of the ridges), the source diagnosticity of the open 

647 field also increases.

648

649 5.8.2. Minutiae: 

650

651 5.8.2.1. Search Diagnosticity:

652

653 5.8.2.1.1. In regions where growth stresses “force” minutiae to form, there 

654 tends to be a high density of minutiae that share direction (the 

655 transition zone from the hypothenar into the mid-palm region is 

656 one such zone). This concept is called “pattern force”. For 

657 example, in the outflow of a loop, many ridges are converging, 

658 which necessarily forces many ridge endings as space runs out. 

659 Because the pattern forces these minutiae to form predictably and 

660 their configurations are more common and less random, they are 

661 properly assigned less weight than more randomly distributed 

662 minutiae toward an association between two impressions. The 

663 existence of a cluster of minutiae in a pattern force area tends to 

664 increase the search diagnosticity of these minutiae.

665

666 5.8.2.2. Source Diagnosticity:

667

668 5.8.2.2.1. While the existence of a cluster of minutiae in a pattern force area 

669 tends to increase the search diagnosticity of the cluster of minutiae, 

670 it tends to decrease the source diagnosticity of those minutiae.

671

672 5.8.2.2.2. Typically, as the surface area of skin represented in an impression 

673 increases, so too does the number of minutiae present within the 

674 impression. While the source diagnosticity of a cluster of minutiae 

675 typically increases as the number of minutiae increases, the source 

676 diagnosticity ranges at a given number of minutiae until a 

677 theoretical maximum threshold is achieved (e.g., a rolled 

678 fingerprint). Beneath this theoretical maximum threshold, source 

679 diagnosticity for a given cluster depends on anatomical region, the 

680 density of the minutiae, the direction of the minutiae, the distance 

681 between the minutiae, and the population of donors under 

682 consideration.

683

684 5.8.3. Incipient Ridges: 

685

686 5.8.3.1. Search Diagnosticity:

687

688 5.8.3.1.1. The search diagnosticity for incipient ridges is generally low 

689 because incipient ridges can appear throughout the friction ridge 
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690 skin and, unlike the ridges and minutiae, are not generally subject 

691 to pattern force.

692

693 5.8.3.2. Source Diagnosticity:

694

695 5.8.3.2.1. In general, as the number of incipient ridges within an impression 

696 increases, the source diagnosticity of the impression also increases.

697

698 5.8.4. Dissociated Ridges: 

699

700 5.8.4.1. Search Diagnosticity:

701

702 5.8.4.1.1. The search diagnosticity for dissociated ridges is generally low 

703 because dissociated ridges can appear anywhere in the friction 

704 ridge skin.

705

706 5.8.4.2. Source Diagnosticity:

707

708 5.8.4.2.1. In general, as the number of dissociated ridges within an 

709 impression increases, the source diagnosticity of the impression 

710 also increases.

711

712 5.8.5. Ridge flow: 

713

714 5.8.5.1. Search Diagnosticity:

715

716 5.8.5.1.1. The search diagnosticity of ridge flows is generally high because 

717 the ridge flows follow a predictable distribution in the human 

718 population for each region of the friction ridge skin. The search 

719 diagnosticity of a ridge flow is elevated when additional features 

720 are present (e.g., shape or regular creases).

721

722 5.8.5.2. Source Diagnosticity:

723

724 5.8.5.2.1. Generally, the source diagnosticity of ridge flows is low. Ridge 

725 flows tend to show significant left/right symmetry within a person. 

726 This symmetry is more pronounced within the corresponding 

727 hands of monozygotic twins.

728

729 5.8.6. Pattern Elements – Recurves and Triradii: 

730

731 5.8.6.1. Search Diagnosticity:

732

733 5.8.6.1.1. The search diagnosticity of pattern elements is generally high 

734 because patterns follow a predictable distribution in the human 

735 population for each region of the friction ridge skin. The search 
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736 diagnosticity of pattern elements is elevated when additional 

737 features are present (e.g., shape or regular creases).

738

739 5.8.6.2. Source Diagnosticity:

740

741 5.8.6.2.1. The source diagnosticity of pattern elements is generally low. 

742 Patterns tend to show significant left/right symmetry within a 

743 person. This symmetry is more pronounced within the 

744 corresponding hands of monozygotic twins.

745

746 5.8.6.2.2. The source diagnosticity of a pattern element or group of pattern 

747 elements depends on the region of skin within which it resides. For 

748 instance, whorls are less common in the interdigital regions of 

749 palms than the interdigital regions of feet.

750

751 5.8.7. Regular Creases: 

752

753 5.8.7.1. Search Diagnosticity:

754

755 5.8.7.1.1. The search diagnosticity of the regular creases is generally high 

756 because the regular creases follow a predictable distribution in the 

757 human population for each region of the friction ridge skin. The 

758 search diagnosticity of a regular crease is elevated when additional 

759 features are present (e.g., shape or ridge flows).

760

761 5.8.7.2. Source Diagnosticity:

762

763 5.8.7.2.1. The source diagnosticity of the number, configuration, and position 

764 of the regular creases is generally low. These attributes tend to 

765 show significant left/right symmetry within a person. This 

766 symmetry is more pronounced within the corresponding hands of 

767 monozygotic twins.

768

769 5.8.7.2.2. The source diagnosticity of the width, length, curvature, and 

770 direction of the regular creases is low to moderate. These attributes 

771 often show significant left/right symmetry within a person and 

772 similarity within the corresponding hands of monozygotic twins.

773

774 5.8.7.2.3. The source diagnosticity of the edge shapes and branching of a 

775 crease is expected to range from moderate to high. These attributes 

776 can show significant left/right symmetry within a person and 

777 similarity within the corresponding hands of monozygotic twins.

778

779 5.8.8. Irregular Creases: 

780

781 5.8.8.1. Search Diagnosticity:
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in Friction Ridge Examination

782

783 5.8.8.1.1. The search diagnosticity of the number, density, width, length, 

784 curvature, and direction of irregular creases depends on the region 

785 of skin under consideration. The search diagnosticity of these 

786 attributes is higher for thenars of palms, proximal and medial 

787 phalanges of the fingers, and the arches of the feet because a high 

788 density of creases is expected in these regions. Elsewhere in the 

789 friction ridge skin the irregular creases are more variable, and 

790 consequently less useful for search diagnosticity.

791

792 5.8.8.2. Source Diagnosticity:

793

794 5.8.8.2.1. The source diagnosticity of the number, density, width, length, 

795 curvature, and direction of irregular creases depends on the region 

796 of skin considered. The source diagnosticity is lower for palm 

797 thenars, proximal and medial phalanges of the fingers, and the 

798 arches of the feet because a high density of creases is expected in 

799 these regions. Elsewhere in the friction ridge skin the irregular 

800 creases are more variable, and consequently displaying higher 

801 source diagnosticity.

802

803 5.8.8.2.2. The source diagnosticity of the branching and angles of 

804 intersection of irregular creases is expected to range from moderate 

805 to high. These attributes can show significant left/right symmetry 

806 within a person and similarity within the corresponding hands of 

807 monozygotic twins.

808

809 5.8.9. Wrinkles: 

810

811 5.8.9.1. Search Diagnosticity:

812

813 5.8.9.1.1. The search diagnosticity for wrinkles is generally low because 

814 wrinkles can appear anywhere in the friction ridge skin.

815

816 5.8.9.2. Source Diagnosticity:

817

818 5.8.9.2.1. In general, as the number of wrinkles within an impression 

819 increases, the source diagnosticity of the impression also increases.

820

821 5.8.10. Scars: 

822

823 5.8.10.1. Search Diagnosticity:

824

825 5.8.10.1.1. The search diagnosticity for scars is generally low because scars 

826 can appear anywhere in the friction ridge skin.

827
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in Friction Ridge Examination

828 5.8.10.2. Source Diagnosticity:

829

830 5.8.10.2.1. In general, as the number or complexity of a scar within an 

831 impression increases, the source diagnosticity of the impression 

832 also increases.

833

834 5.8.11. Unstable features: 

835

836 5.8.11.1. Search Diagnosticity:

837

838 5.8.11.1.1. The search diagnosticity for unstable features is generally low 

839 because unstable features can appear anywhere in the friction ridge 

840 skin.

841

842 5.8.11.2. Source Diagnosticity:

843

844 5.8.11.2.1. In general, as the number or complexity of an unstable feature 

845 within an impression increases, the source diagnosticity of the 

846 impression also increases.

847

848 5.8.12. Shape of the Impression: 

849

850 5.8.12.1. Search Diagnosticity:

851

852 5.8.12.1.1. The search diagnosticity of size and outline of an impression is 

853 generally high because the size and contours of human hands and 

854 feet are generally shared in the population. The search 

855 diagnosticity of an impression’s shape is elevated when additional 

856 features are present (e.g., ridge flows or regular creases).

857

858 5.8.12.2. Source Diagnosticity:

859

860 5.8.12.2.1. The source diagnosticity of the shape of an impression is low. 

861 Hands and feet tend to show significant left/right symmetry within 

862 a person and similarity within the corresponding hands of 

863 monozygotic twins.

864

865

866
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in Friction Ridge Examination

867 6. Appendix A: Edge Shapes

868 The images below highlight the edge shapes on normal ridges; however, these shapes can also 

869 occur on segmented ridges (dysplasia) or incipient ridges.

870

Edge Shape Description Example

Straight Where the edge of the ridge is defined by a 

smooth line.

Protrusion Where the edge of the ridge protrudes into 

the furrow (causes a widening of the ridge at 

that location).

Intrusion Where the edge of a ridge intrudes into the 

main body of the ridge (causes a narrowing 

of the ridge at that location).

871 Table 1 - Examples of edge shapes (images not to scale)

872

873

874

875

876

877

878

879

880
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in Friction Ridge Examination

881 7. Appendix B: Minutiae

882 Simple Minutia Types

Minutia Type Definition Example

Ending Ridge The end of a ridge with no 

connection to the adjacent 

ridge above the level of the 

furrow.

Bifurcation The complete connection of an 

end of a ridge to the adjacent 

ridge from the bottom of the 

furrow to the top of the ridge

Ambiguous 

Minutia 

The partial connection of the 

end of a ridge to the adjacent 

ridge (connected above the 

level of the furrow, but below 

the level of the tops of the 

ridges)

883 Table 2 - Examples of simple minutiae (images not to scale)

884

885 Compound Minutia Types

Minutia Type Definition Example

Short Ridge An independent ridge (defined by two ending 

ridges) with a length that is less than ten times the 

average width of the ridge.

Dot An independent ridge with a length that is less than 

two times the average width of the ridge.
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Minutia Type Definition Example

Break A site along the ridge where the course of the ridge 

is interrupted, like a sink hole in the ridge. This 

length of the discontinuity is at least the width of the 

ridge, but no longer than twice the width of the 

ridge.

Enclosure A minutia defined by the merger of both ends of a 

short ridge with a neighboring ridge (defined by two 

bifurcations directed toward each other). The 

distance between the bifurcations is less than ten 

times the average width of the ridges.

Overlap Where two ridges meet and overlap. The length of 

overlap is less than ten times the average width of 

the ridges.

Spur A minutia defined by the merger of one end of a 

short ridge with a neighboring ridge (defined by one 

bifurcation and one ending ridge). The distance 

between the ending ridge and bifurcation is less than 

ten times the average width of the ridges.

Crossbar A ridge that alters its course to zig-zag around other 

minutiae, similar to a train switching tracks. The 

transfer zone is less than ten times the average 

width of the ridges.

Bridge A minutia defined by the merger of a short ridge 

with two neighboring ridges. The path of the bridge 

tends not to be parallel to the neighboring ridges 

and the length of the bridge is no longer than five 

times the average width of the ridges.

Opposing 

Bifurcations

A minutia defined by two bifurcations directed 

away from each other. The distance between the 

two bifurcations is less than five times the average 

width of the ridges.
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Minutia Type Definition Example

Dock A minutia defined by an overlapping cluster of three 

ridge endings where the center ridge ending is in the 

opposite direction of the other two ridge endings

and the length of overlap on each side of the center 

ridge is less than ten times the average width of the 

ridges.

Ending Ridge + 

Bifurcation 

Combination

A minutia defined by the end of a ridge leading to a 

bifurcation. The distance between the end of the 

ridge and the bifurcation is less than five times the 

average width of the ridges.

Trifurcation/Double 

Bifurcation

A minutia defined by the merger of three ridges into 

one. This minutia type can appear as a trifurcation 

when the three ridges emanate from a common 

vertex or a double bifurcation when one ridge is not 

centered on a vertex with the other two ridges. The 

merger of the three ridges is contained within a 

distance less than three times the average width of 

the ridges.

Return The location along an independent ridge where the 

ridge makes a 180o turn and the return is not part of 

a recurve associated with a tented arch, loop or 

whorl pattern.

Merge Point The merger of the legs of two bifurcations into one 

ridge. The mergers (the points of the “M”) are 

contained within a distance less than five times the 

average width of the ridges.

886 Table 3 - Examples of compound minutiae (images not to scale)

887

888

889

890

891

892

893

894
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895

896 8. Appendix C: Incipient Ridges and Dissociated Ridges

Feature Example

Incipient ridges in the friction ridge skin of a

finger

Incipient ridges in an impression of a finger

Incipient ridges in an impression of a palm

Incipient ridges in an impression of a foot

Dissociated ridges (severe case) in an 

impression of a palm 
OSAC 2022-S-0038 Standard for Feature Selection

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Feature Example

Dissociated ridges (severe case) in an 

impression of the distal and medial segments 

of the fingers

Dissociate ridges (mild case) in an impression 

of a thumb

897 Table 4 - Examples of incipient ridges and dissociated ridges (images not to scale)

898

899
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900 9. Appendix D: Pattern Elements

901 The patterns below are defined at a very rudimentary level to permit the use of pattern definitions 

902 across regions of the friction ridge skin. It is recognized that there are various classification 

903 schemes, with different rules, related to each region of the friction ridge skin. 

904

905 In partial impressions of the friction ridge skin; however, it is not always possible to determine if 

906 a given pattern (e.g., a loop) is from a specific anatomical region. If the anatomical region cannot 

907 be determined, it is impossible to know which classification scheme to apply or the specific rarity 

908 of the pattern (i.e., a triradius is rarer in the hypothenar than the interdigital of a palm). It is 

909 recognized that some patterns on the skin do not easily conform to the below categories and this 

910 standard will not attempt to catalog each permutation of the patterns that are possible in the friction 

911 ridge skin. 

912

913 In this table, all impressions are oriented distally. Isolating each pattern and providing examples 

914 from each region of the skin highlights the importance of relationships between the patterns (e.g., 

915 position of the triradius in relation to the recurve of a loop) and other features to assess the

916 anatomical region and orientation.

917

Pattern Examples

Triradius 

Three rays of ridges 

(convergence of three 

ridge fields) that 

converge on a 

geometric center point. 

The core of a triradius is 

the geometric center 

point.

Distal Segments of Fingers

 Medial and Proximal Segments of Fingers

 

Palms

 

Soles

 

Toes
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Pattern Examples

 

Tented Arch 

A triradius with a 

recurve over one of the 

rays (the ray can be one 

or more ridges). The 

core of the tented arch is 

the geometric center 

point of the triradius.

Fingers

 

Palms

 

Soles

 

Toes

 

Loop 

A pattern defined by a 

single recurve in the 

ridges that does not arch 

over a radius. The core 

is generally positioned 

on the sharpest curve 

along the innermost 

recurve.

Distal Segments of Fingers

 

Palms

 
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Pattern Examples

 

Toes

 

Soles

 

Whorl

A pattern defined by 

two or more recurves, 

making a roughly 

circular pattern of 

ridges. While biometric 

systems may have 

specific rules for 

indicating the core of a 

whorl in fingers, these 

rules do not apply for 

palms and feet. 

Consequently, friction 

ridge examiners can use 

alternative or multiple 

cores when considering 

whorls.

Distal Segments of Fingers

 

Palms

 

Toes

 
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Pattern Examples

Soles

 

 

Column

Two triradii flanking 3 

or more ridges that are 

parallel to the rays of 

the triradii. The core of 

the column is the 

center-most ridge 

between the two 

triradii.

Medial and Proximal Segments of Fingers

Palms

 

Soles

 

Vestige Thenars of Palms 
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Pattern Examples

A complex pattern 

associated with the 

distal portion of the 

thenars of the palms.

 

918 Table 5 – Examples of patterns in the hands and feet.
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in Friction Ridge Examination

919 10.Appendix E: Ridge Flows

920

921

922 Figure 1 - Hand Ridge Flows. Hands not to scale.
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923

924 Figure 2 - Foot Ridge Flows. Feet not to scale.

925
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in Friction Ridge Examination

926

927 11.Appendix F: Regular and Irregular Creases of the Hands and 

928 Feet

929

930 Figure 3 - Regular and irregular creases of the palm (image not to scale).

931 Regular Creases: DIC – Distal Interphalangeal Crease; PIC – Proximal Interphalangeal Crease; 

932 PDC – Palmar Digital Crease; DTC – Distal Transverse Crease; PTC – Proximal Transverse 
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in Friction Ridge Examination

933 Crease; TC – Thenar Crease; WC – Wrist Crease. The remaining “white lines” in the hand 

934 impression are irregular flexion creases. 

935

936

937 Figure 4 - Regular and Irregular creases of the foot (image not to scale).
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in Friction Ridge Examination

938 Regular creases: DIC – Distal Interphalangeal Crease; PIC – Proximal Interphalangeal Crease; 

939 PDC – Plantar Digital Crease. The remaining “white lines” in the foot impression are irregular 

940 flexion creases. 

941
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in Friction Ridge Examination

942 12.Appendix G: Wrinkles

943

Feature Example

Wrinkles in the friction ridge skin

 

944 Table 6 - Examples of wrinkles (images not to scale)

945

946

947 Figure 5 - The right thumb and fingers of a subject taken 39 years apart (images not to scale). 

948 The additional "white lines' in 2008 impressions are wrinkles acquired over the 39-year period.

949
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in Friction Ridge Examination

950 13.Appendix H: Scars

Feature Example

Simple scar in the friction ridge 

skin

Burn in the friction ridge skin

Impressions of the same finger 

before and after the formation 

of a complex scar with 

epithelial islands

 

951 Table 7 - Examples of scars (images not to scale).

952
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in Friction Ridge Examination

953 14.Appendix I: Unstable Features

954 The examples below are not an exhaustive list of unstable features, but those unstable features 

955 seen most commonly in the friction ridge skin.

956

Feature Example

Actively healing cuts on the friction 

ridge skin (this feature is considered 

unstable until the healing process is 

complete and it may, or may not, 

result in a detectible scar)

Actively healing scrapes in an 

impression of a finger taken in 2007 

and the recovery of the skin in 2008 

(two stable scars highlighted in 

yellow)

Callus in the interdigital of a palm

Calluses in an impression of a right 

interdigital palm
OSAC 2022-S-0038 Standard for Feature Selection

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Feature Example

Wart in the friction ridge skin

Wart in an impression of a finger

Eczema/psoriasis in an impression of 

a finger

957 Table 8 - Eczema/psoriasis in an impression of a finger

958
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

959 15.Appendix J: Relationship of Features

960 Throughout the descriptions of the various features in this standard, reference is made to the impact 

961 of feature attributes, and relationships between features, on the search diagnosticity and source 

962 diagnosticity. This section provides examples of relationships and their potential impact on the 

963 examination process. 

964 Example 1: In the series of images below the colors signify the following features: green is the 

965 relevant outline of the impression, blue indicates patterns (including triradii), purple indicates ridge 

966 flow, yellow indicates regular crease. In each image, more of the impression is revealed to 

967 demonstrate the importance of the relationships of these features and how these relationships guide 

968 decisions. The feature discussion illustrates the thought process, it is not an example of expected 

969 documentation for the impression.

Feature Discussion Impression

The relationship of the size and outline of this 

impression and the position of the triradius within the 

surrounding ridge flow rule out fingers and toes but 

include the palms and feet as a possible donor region. 

The shape of the impression and the triradius angles 

further indicate the impression is in the most likely 

distal orientation and most likely from an interdigital 

region of a palm or foot.

The shape (size and outline) indicates the interdigital 

region of a palm or foot. The pattern relationships 

between the two triradii (ridge count and angle), the 

curvature of the ridge flows, the divergence and 

convergence (going from top to bottom) of the ridge 

flow between the triradii, and the presence of the 

palmar/plantar digital crease also indicate interdigital 

region of a palm or foot. The triradius angles of the two 

triradii and their respective relationships to the 

perimeter of the impression and palmar/plantar digital 

crease indicate possible left interdigital palm under the 

index and middle fingers or a left foot under the great 

toe and index toe. A right interdigital palm under the 

little and ring fingers and a right interdigital foot under 

the little and ring toes cannot be ruled out.
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Feature Discussion Impression

The shape (size and outline) indicates the interdigital 

region of a palm or foot. The relationships between the 

three triradii, the ridge flows (curvature, divergences 

and convergences), and palmar/plantar digital crease 

also indicate interdigital region of a palm or foot. The 

triradius angles of the left and middle triradii and the 

surrounding ridge flows indicate these patterns are 

positioned under the middle and ring digits of a left 

interdigital palm or the index and middle digits of a left 

interdigital foot. The triradius angles of the right 

triradius and the surrounding ridge flows indicate this 

pattern is located under the index finger of a left palm 

or the great toe of a left foot. Given the size of the 

impression, the lack of a visible distal transverse crease 

indicates this impression is more likely from a left foot 

rather than a left palm.

The following features and their various relationships 

to each other are consistent with an impression from a 

left foot and toes: shape (size and outline), regular 

creases, patterns (including triradii), and distinct ridge 

flows.

970 Table 9 – Examples of the diagnosticity of feature relationships (images to scale).

971 Example 2: This example describes two impressions of the friction ridge skin, each with a different 

972 subset of features present. The colors signify the following features: green is the relevant outline 

973 of the impression, blue indicates patterns (including triradii), purple indicates ridge flow, yellow 

974 indicates regular crease, and orange indicates a possible irregular crease. The discussion below 

975 each image illustrates the thought process and the importance of the friction ridge examiner’s 

976 understanding of the distribution of the features and feature relationships in the human population. 

977 The feature discussion illustrates the thought process, it is not an example of expected 

978 documentation for the impression.
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Impression A Impression B

The shape (size and outline) of impression A in 

combination with the ridge flow indicates this 

impression could have originated from any 

region of the friction ridge skin; however, the 

distal portion of any of the digits is unlikely. The 

combination of the limited features also indicates 

multiple orientations would have to be 

considered and fully recorded friction ridge 

impressions of both the hands and feet would be 

required to exclude a given person.

The source diagnosticity of the ridges and 

minutiae (and their attributes) should be 

impacted by the inability to pinpoint the 

anatomical region and orientation of Impression 

A. In other words, is this cluster of ridges and 

minutiae (and their various attributes) sufficient 

given the unknown anatomical region and 

orientation of this impression? 

The following features, attributes, and 

relationships indicate Impression B should be 

oriented as indicated above and represents a right 

interdigital palm below the middle and ring 

fingers and the proximal segment of the right 

middle finger: shape (size and outline), patterns 

(including triradii), ridge flows, and regular 

flexion crease. 

The ability to pinpoint the specific hand and 

region of the hand is dependent on the friction 

ridge examiner’s understanding of the 

distribution of these features in normal human 

hands and feet. The combination of features in 

Impression B could be considered so diagnostic 

for source; however, that the inability to pinpoint 

anatomical region and orientation (which 

indicates many more possible donor regions) may 

not significantly influence the source 

diagnosticity of the impression.

979 Table 10 - Examples of the diagnosticity of feature relationships.

980
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

981 16.Appendix K: Quick Reference Summary Table

Attributes Search Diagnosticity Source Diagnosticity

Ridges § Number

§ Ridge Width

§ Furrow Width

§ Length 

§ Spacing 

§ Direction 

§ Curvature 

§ Edge Shapes

§ Pore Position 

§ Open Field 

Low § In general: surface area increases, 

source diagnosticity increases

§ In general: open field increases in 

size, source diagnosticity of the open 

field increases

Minutiae § Number

§ Density

§ Direction 

§ Connectedness 

§ Compound Minutiae 

Cluster of minutiae in a pattern force 

area generally increases search 

diagnosticity

Cluster of minutiae in a non-pattern 

force area generally decreases search 

diagnosticity

§ In general: number increases, source 

diagnosticity increases

§ Minutiae in a pattern force area can 

decrease source diagnosticity

§ For a given cluster: depends on 

anatomical region, density of the 

minutiae, direction of the minutiae, 

distance between the minutiae, 

population of donors under 

consideration

Incipient Ridges § Number

§ Density

§ Width

§ Length

§ Direction

§ Inter-Incipient Break

Low § In general: number increases, source 

diagnosticity increases
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Attributes Search Diagnosticity Source Diagnosticity

§ Edge Shapes

Dissociated Ridges § Number 

§ Density

§ Ridge Width

§ Furrow Width

§ Length

§ Spacing

§ Direction

§ Curvature

§ Edge Shapes

§ Pore Position

§ Connectedness

Low § In general: number increases, source 

diagnosticity increases

Ridge Flows § Curvature

§ Convergence

§ Divergence

High, elevated in combination with 

additional features (e.g., shape or 

regular creases)

§ Low

Pattern Elements: 

Recurves and Triradii

§ Number

§ Triradius Angle

§ Core Ridge Count

§ Core Length

§ Pattern Element

Relationships

High § Low

§ Value depends on the region of skin

Regular Creases § Number

§ Configuration

§ Spacing

§ Position

§ Width

§ Length

§ Curvature

§ Direction

§ Edge shapes

High § Low (number, configuration, 

position)

§ Low to moderate (width, length, 

curvature, direction)

§ Moderate to high (edge shapes, 

branching)
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Attributes Search Diagnosticity Source Diagnosticity

§ Branching

Irregular Creases § Number

§ Density

§ Width

§ Length

§ Curvature

§ Direction

§ Branching

§ Angle of intersection

§ Spacing

Depends on the region of skin (higher 

in the thenars of palms, proximal and 

medial phalanges of the fingers and 

arches of feet)

§ Lower in palm thenars, proximal and 

medial phalanges of the fingers, 

arches of the feet

§ Higher in other regions of skin

Wrinkles § Number

§ Density

§ Width

§ Length

§ Curvature

§ Direction

§ Branching

§ Angles of intersection

§ Spacing

Low § More wrinkles, higher source 

diagnosticity

Scars § Number

§ Width

§ Length

§ Surface Area

§ Curvature

§ Direction

§ Created Minutiae

§ Edge shapes

Low § The more complex and frequent, the 

higher the source diagnosticity

Unstable Features § Number

§ Width

§ Length

Low § The more complex and frequent, the 

higher the source diagnosticity
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

Attributes Search Diagnosticity Source Diagnosticity

§ Surface Area

§ Curvature

§ Direction

§ Branching

§ Edge shapes

Shape of the 

Impression

§ Surface area

§ Outline

High Low

982 Table 11 – Quick Reference Summary Table

983
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

984 17.Appendix L: References

985 1.1. Babler, W. Embryological Development of Epidermal Ridges and Their 

986 Configurations. Birth Defects Original Article Series 1991 27 (2), 95-112.

987 1.2. Champod, C.; Lennard, C.; Margot, P.; Stoilovic, M. Fingerprints and Other Ridge 

988 Skin Impressions, Second Edition. CRC Press: New York, 2016. 

989 1.3. Drahansky, M.; Dolezel, M.; Urbanek, J.; Brezinova, E.; Kim, T. Influence of Skin 

990 Diseases on Fingerprint Recognition. Journal of Biomedicine and Biotechnology

991 2012, 626148. DOI: 10.1155/2012/626148.

992 1.4. Fox, K.; Plato, C. Toe and Plantar Dermatoglyphics in Adult American Caucasians. 

993 American Journal of Physical Anthropology 1987 74 (1), 55-64.

994 1.5. Gutiérrez, E.; Galera, V.; Martínez, J.M.; Alonso, C. Biological Variability of the 

995 minutiae in the Fingerprints of a Sample of the Spanish Population. Forensic Science 

996 International 2007 172, 98-105. DOI: 10.1016/j.forsciint.2006.12.013

997 1.6. Gutiérrez-Redomero, E.; Alonso-Rodríguez, C.; Hernández-Hurtado, L.; Rodríguez998 Villalba, J. Distribution of the Minutiae in the Fingerprints of a Sample of the Spanish 

999 Population. Forensic Science International 2011 208, 79-90. DOI: 

1000 10.1016/j.forsciint.2010.11.006

1001 1.7. Holt, S. The Genetics of Dermal Ridges. Charles Thomas Publisher: Illinois, 1968.

1002 1.8. Kimura, S.; Kitagawa, T. Embryological Development of Human Palmer, Plantar, 

1003 and Digital Flexion Creases. The Anatomical Record 1986 216 (2), 191-197.

1004 1.9. Kimura, S.; Schaumann, B.; Shiota, K. Comparative Investigations of Human and Rat 

1005 Dermatoglyphics: Palmar, Plantar and Digital Pads and Flexion Creases. Anatomical 

1006 Science International 2002 77 (1), 34-46.

1007 1.10. Kong, A.; Zhang, D.; Lu, G. A Study of Identical Twins’ Palmprints for Personal 

1008 Identification. Pattern Recognition 2016 39 (11) 2149-2156. DOI: 

1009 10.1016/j.patcog.2006.04.035.

1010 1.11. Lin, C.H.; Liu, J.; Osterburg, J.; Nicol, J. Fingerprint Comparison I: Similarity of 

1011 Fingerprints. Journal of Forensic Science 1982 27 (2), 290-304.

1012 1.12. Mavalwala, J.; Mavalwala, P.; Kamali, S.M. Dermatoglyphics and Population 

1013 Distance. In Trends in Dermatoglyphic Research; Durhan, D., Plato, C., Eds.; 1990, 

1014 Kluwer Academic Publishers: Boston, 1990; 190-199.

1015 1.13. Meier, R. Anthropological Dermatoglyphics: A Review. Yearbook of Physical 

1016 Anthropology 1980 23 (S1), 147-178.

1017 1.14. Neumann, C.; Champod, C.; Yoo, M.; Genessay, T. Quantifying the Weight of 

1018 Fingerprint Evidence through the Spatial Relationship, Directions, and Types of 

1019 Minutiae Observed on Fingermarks. Forensic Science International 2015 248, 154-

1020 171. DOI: 10.1016/j.forsciint.2015.01.007

1021 1.15. Okajima, M. Dermal and Epidermal Structures of the Volar Skin. Birth Defects: 

1022 Original Article Series 1979 XV (6), 179-198.

1023 1.16. Pandey, A.; Sharma, A. Formulation of Longitudinal Flexion Creases: Validation of 

1024 Inheritance, Twin Diagnosis and Ethnic Variation. International Journal of Science 

1025 and Research 2016 5 (4) 2296-2300.
OSAC 2022-S-0038 Standard for Feature Selection

in Friction Ridge Examination

1026 1.17. Pandey, A.; Sharma, A. Formulation of Transverse Flexion Creases: Validation of 

1027 Inheritance, Twin Diagnosis and Ethnic Variation. Journal of Humanities and Social 

1028 Science 2016 21 (5), 41-49.

1029 1.18. Shaumann, B.; Alter, M. Dermatoglyphics in Medical Disorders. Springer-Verlag: 

1030 New York 1976.

1031 1.19. Stücker, M.; Geil, M.; Kyeck, S.; Hoffman, K.; Röchling, A.; Memmel, U.; Altmeyer, 

1032 P. Interpapillary Lines – The Variable Part of the Fingerprint. Journal of Forensic 

1033 Science 2001 46 (4), 857-861.

1034 1.20. Tao, X.; Chen, X.; Yang, X; Tian, J. Fingerprint Recognition with Identical Twin 

1035 Fingerprints. PLoS ONE 2021 7 (4), e35704. DOI: 10.1371/journal.pone0035704.

1036 1.21. White, A. Features of the Friction Ridge Skin: Attributes, Diagnosticity, and 

1037 Limitations. Journal of Forensic Identification 2022 72(1) 33-127.

1038 18.Appendix M: Change Log

Version Date Change

1.0 09/06/2022 Original Issue

1039