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APR IV B69

NBS TECHNICAL NOTE

481

A Semi-automated Single Fingerprint

Identification System

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U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 481

ISSUED APRIL 1969

A Semi-automated Single Fingerprint

Identification System

J. H. Wegstein

Center for Computer Sciences and Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, Government Printing Office Washington, D.C, 20402 - Price 30 cents
Contents

Page

1. Introduction 1

2. Objectives of the system 2

3. Instructions for coding a fingerprint 3

4. Computer procedure for reading and filing

codes —----- 4

5. Procedure for comparing codes 5

6. Preliminary results and discussion 6

7. Conclusion 7

3. References 8

II
A Semi- automated Single Fingerprint

Identification System

by J. Ho Wegstein

A system is described in which a fingerprint is

manually coded by tracing certain ridges and noting events

such as ridge endings and ridge beginnings. This code is

sent by teleprinter to a central file where a computer

identifies the fingerprint by comparing the code with

codes previously entered in the file. The scheme for

comparing codes is given along with some preliminary test

results using typical fingerprints.

Key words: Computerized- fingerprint identification,

fingerprints, pattern-recognition

lo Introduction

The Ninth Session of the International Police Conference held in

New York in 1923 adopted a system for identifying individuals using

information from single fingerprints. This system, called Distant

Identification, was developed by Hakon Jorgensen and utilized about

fifty numerals of coded fingerprint information which could be transmitted by telephone, telegraph, or radio.

About the same time Scotland Yard began testing a similar system

by C.S. Collins . In both of these systems the coded information from

fingerprints was obtained with a magnifying glass using a special

reticle containing two parallel lines. In the Collins system the

parallel lines were 6 mm apart and in the Jorgensen system the lines were 4 mm apart. In addition to information about the core of the

fingerprint, the codes also included topological information from the

ridges observed between the parallel lines of the reticle resting at

a prescribed position on the fingerprint.

At Scotland Yard the Collins system was tested on a collection

including some 40,000 single prints representing about 4,000 persons.

It was found that the codes did not discriminate adequately between

like and unlike prints, and it was necessary in many cases to examine

not less than 75 per cent of the impressions filed under the particular

type of pattern for which the search was being made. During a period

of seven years only a very few identifications were made .

Another single fingerprint identification system was developed by

Battley4 at Scotland Yard which was intended to augment the Henry

system for dealing with latent fingerprints found at the scene of a crime. The Battley system deals with coded core information along with

delta positions, ridge counts, ridge traces and other peculiarities of

the printo A special reticle with concentric circles is used for defining areas for scrutiny in the fingerprint.
The success of any of these single fingerprint identification

systems has been limited, and several reasons for this might be

identified as follows: (a) Searching files of codes manually is

difficult and slow. (b) The skill required to code the fingerprints

may have limited the number of users. (c) The technique may have had

an insufficient ability to discriminate between like and unlike prints,

(d) The system lacks an adequate scheme for ordering or classifying

the codes.

Most of the fingerprint systems developed to date utilize

topological techniques such as core pattern descriptions, ridge counts

and ridge tracing. They also utilize geometrical techniques such as measurements on the print and determining where to count ridges.

Geometrical techniques suffer from the stretching and flexing of

fingerprints, and topological techniques such as core pattern

descriptions suffer from the variation in the inking of fingerprint

impressions as well as the amount of training required by the user. Hankley and Tou have investigated purely topological coding and

concluded that it should be feasible to automatically trace ridges and

topologically code fingerprints.

The system described in this paper attempts to strike a good

balance between the geometrical and topological techniques used. It

limits its objectives by not attempting to deal with latent prints,

and most important of all, it utilizes a computer for searching a fingerprint file and matching fingerprint codes. The use of the

computer has permitted the code for the fingerprint to be easily

written by an individual with limited fingerprint experience.

2, Objectives of the System

In this system it is assumed that a central computer will maintain

a file consisting of the codes for two fingerprints from each of several

thousand fugitives or persons wanted by police. At some remote

location the two appropriate fingerprints can be taken from a suspected

person. The codes for these fingerprints can be determined in about ten

minutes using a special reticle with a regular fingerprint magnifying

glass. (An opaque projector with an enlarged reticle is of course

easier to use,) These codes are then sent to the central computer via

a directly connected remote teleprinter or by radio or telephone to an operator at such a typewriter. The computer compares these codes with

those in the file and computes a score indicating how well these codes

match each of those in the appropriate section of the file. If the score is above a certain threshold value, the computer reports the

probable identity of the suspect back to the inquirer.

An enlargement of the reticle used by this system is shown in

Figure 0. The horizontal lines are 13 mm apart and the radial lines are 18° apart.
3. Instructions for Coding a Fingerprint

Orienting Reticle

Set the horizontal lines of the reticle parallel with the crease

in the finger

Locating Origin

The upper horizontal line of the reticle is placed on the lowest

full ridge that is smoothly convex upward, that is, just above the

highest core. See examples in Figure 1.

On a plain arch where no core pattern such as those shown in

Figure 1 occurs, set the intersection of the vertical line and the

lower horizontal line at the middle of the crease in the finger.

Next, move the reticle up or down slightly so that the upper horizontal line falls on the nearest ridge.

The intersection of the vertical line and upper horizontal line

should be at the highest point of the ridge.

Coding the Print

Starting with the first ridge above the (upper) horizontal line

and moving upward, the successive ridges that cross the vertical line are numbered 1, 2, 3, etc„ through 14.

Each ridge is traced from left to right starting at the horizontal

line on the left and ending at the horizontal line on the right. As

one follows the ridges from left to right, events are coded as follows:

ridge runs all the way from the horizontal line on the left to

the horizontal line on the right. See Figure 2 for such ridge

patterns and their codes. Ridges that cross the vertical line are called reference ridges and are given integral line numbers.

e ridge ends before it reaches the horizontal line on the right.

The position at which the ridge ends is indicated by the sector

number. Thus ridge number 3 ends in sector 7 in Figure 3o If

a ridge does not cross the vertical line it is given a decimal

line number. See ridge 3»1 in Figure 4. A ridge that rejoins

a lower ridge is also called a ridge ending. See ridge 3 in

Figure 5.

s a ridge starts. See ridge 5 in Figure 5„ The point where a ridge departs from a lower ridge is also called a starting ridge.

Thus, ridge 7» 1 starts in sector 8 in Figure 5.
i an island or short ridge whose length does not exceed a sector

length. See code line 8.1 in Figure 5.

An enclosure, spur, closure between ridges, or notable lump on a ridge is also coded as i if such event does not exceed a sector length.

Several examples are given in Figure 6„ If one of these events falls

on a sector line, such as code line 4.1 or 10.1 in Figure 6, it is

given the sector number corresponding to where it starts. The line

number of an event occurring between ridges is obtained by referring to

the next lower ridge. Note that spurs hanging below a ridge are referred to the next lower ridge by line number. See line 7. 1 in

Figure 6„ Enclosures and spurs projecting upward are referred to the

ridge to which they are attached.,

A break in a ridge that is shorter than a sector length is not

coded. See ridge 5 in Figure 6. Islands separated by less than a sector length are treated as continuous ridge. Incipient ridges are

ignored. When a section of ridge does not cross the horizontal line,

its start and end are both given in a code line separated by a comma. For examples, see lines 7.1 and 7.2 in Figure 7.

Figures 7 through 10 demonstrate the order in which events are

coded. Events are coded from a reference ridge outward as they are noted in reading from left to right. Thus in Figure 8, following

ridge 5, ridge 5.1 ending in e3 is followed by ridge 5.2 starting in

s7, and this is followed by 5.3 ending in el. Ridge 5.3 may be

thought of as having higher rank, than 5.1 and 5.2 because it is further

from the reference ridge 5.

Note that the line numbers correspond to the ridge count along the

vertical line. Nothing is coded ahead of ridge 1. Coding stops when

line numbers reach 14, when an indistinct area is encountered, or when

full ridges fail to reach from the horizontal line on the left to the

horizontal line on the right.

4. Computer Procedure for Reading and Filing Codes

When a code is to be entered into the computer the operator first

indicates whether the codes is to be filed (F) or the code is to be

searched against the existing file (S) . An identification such as a name or police identification number is next typed in followed by the

code. The line numbers are omitted to save time. As an example, the
e7

s8

12

code from Figure 5 would be typed as shown at the left. The

computer treats this code as columns A and B in a table.

Dashes are entered as 00. The line number is re-determined

by the computer without the decimal and stored in column C.

„ The code would now appear as the table shown in Figure 11.

This table is next sorted on column B without otherwise

changing the order of the table so that the table appears as shown in columns A B C of Figure 12 „ This table along with

the identification is compressed in whatever manner suits

the computer and is entered in the file or else it is held

in readiness for comparing with other tables from the file.

5. Procedure for Comparing Codes

Assume that a match for Figure 5 is being sought from a file which

already contains the table of data corresponding to Figure 10„ When

the computer is ready to compare Figure 5 with Figure 10, it holds the

table corresponding to Figure 5 as columns A B C of Figure 13 and it

brings the table corresponding to Figure 10 from the file as columns

E F G of Figure 13. (When two tables corresponding to two fingerprints

are being compared, the shortest table is always placed in columns

A B C )

The numbers in columns D and H are initially set equal to zero.

(The details of the computer program for what follows are given in the

Flow Diagram in the Appendix.)

Starting at M=l, step down the rows of table A B C D one at a time.

For each row in table A B C D, sweep down the table E F G H looking for

the following situation: A is identical with E; B and F differ by one

or less; C and G differ by one or less, and H is not one. If this

situation is found , set H equal to one and set D equal to one. If this

situation is not found , do the first of the following which is appropriate: If A is 0, set D equal to -1; If A is "i" or if B is equal to

or 9, leave D equal to zero; otherwise, set D equal to -1.

When the steps in the previous paragraph have been applied to

each row of table A B C D the matching operation is finished,, The

score, S, indicating how well the prints match is obtained by adding

the numbers in column D. In Figure 13, S=3. This score is re-computed

with G increased by one and also decreased by one. (In the computer

program given in the Flow Diagram, this means using Q=0, 1, and -1.)

The final score is taken as the largest of these three scores. This

allows for a difference of opinion by coders as to where ridge counts

should start on the fingerprint. (The matchine procedure allows for an additional difference in opinion as to ridge count as well as sector

number.) A final score equal to or greater than 14 indicates that the

prints probably came from the same finger, but a value for this probability has not been determined.
Figures 14 and 15 show two different impressions taken from the same finger„ The reticle is superimposed and the code for each impression is shown at the right of each figure. Note that the codes do not

exactly agree. For example, the ridge ending, eo, in line 1 1 of

Figure 15 does not occur in the code in Figure 14. Also, the ridge

ending, e3, in line 7.1 of Figure 15 is interpreted as being in code

line 8.1 in Figure 14. However, these differences do not lose points

in the scoring,, The tables generated for comparing these two

impressions are shown in Figure 16. The score, S=26, indicates a veryhigh probability that the impressions are indeed from the same finger,

6. Preliminary Results and Discussion

As a preliminary test of this system, fourteen different fingerprint impressions labeled Wl through W14 were coded directly from cards

and stored in the computer file. The types include ulnar loops LH,

ulnar loops RH, whorl, and double loops „ Fourteen different impressions

from the same fingers respectively (taken from five months to eight

years later) were then coded by a different person and labeled Pi

through P14. These codes were then compared with those in the file

and the resulting scores are given in Figure 17. The scores for two

prints from the same finger appear along the diagonal. If a threshold were set so that any score of 14 or greater would be considered a "make", all of the second set of fingerprint impressions would be

correctly identified except P5 which would claim to be either Wl or

its correct match, W5.

This preliminary data suggests that a single fingerprint might be

used with a suitable threshold score to locate one or more "possibilities"

for an identif ication„

When plain arches are coded it is difficult to determine where to

start counting ridges because of variation in the inking of the crease

in the finger which locates the lower horizontal line of the reticle,,

As above, nine different arches were coded and filed as W15 through W23„

Different impressions of these same fingers were coded by another coder

and searched against the file„ The results, shown in Figure 18,

indicate that single arches are not very satisfactory for use in this

system. The very low score for P18 matched with W18 was found to be

caused by a difference of inking of the crease in the finger,,

The scores in Figure 17 and 18 suggest that using two fingerprints

from an individual instead of one print will produce a higher discrimination. To analyse this, assume that successive pairs of these prints

are from the same person. Thus assume that Wl and W2 are both from

the same person. Pi and P2 would therefore be two different impressions

from the same fingers of this person. The scores of Pi versus Wl equal

to 19 and P2 versus W2 equal to 17 are multiplied together to produce

a new score for this individual, SR=323. Pi versus W3 and P2 versus W4

produce a score of 4 representing a comparison of prints from two

different people. The results of this scoring technique for the loops
and whorls are shown in Figure 19 and the results using arches are shown in Figure 20. With a threshold score of SR=90, every individual

would be correctly identified.

7. Conclusion

From these preliminary results, it appears desirable to use two

fingerprints from each person, for example the two index fingers.

Arches are less reliable than other pattern types. This degradation

could be minimized by systematically skipping arches and using the

prints from other fingers. If this practice were followed, arches

would only be used from those individuals who have no other types

of prints.

Considerably more fingerprints must be processed to answer the

following questions: What threshold score should be used? What is

the probability that an identification is correct? Can police

technicians readily learn to consistently code fingerprints using this

system? When an individual's prints are to be placed in the file,

what is the probability that prints can be found in existing files that are suitable for coding? (When a suspect is in custody the unsuitable

prints can be re-taken.) Can a computer or specially built device

search a file fast enough? This raises a question as to whether

subfiles are needed based on pattern types or whether an ordering or classification scheme can be devised based on the code themselves.

Finally, will the system be useful?

The author is indebted to the Identification Division of the

Federal Bureau of Investigation for its assistance and financial

support of this work. He is indebted for the computer programming

and testing of this system to Mr J.F. Rafferty of the National Bureau

of Standards and to Mr. W.J. Pencak, a Guest Worker at NBS from the

Federal Bureau of Investigation.

This system was tested with the MOBIDIC computer in the NBS

Research Computer Facility. It has been particularly helpful to

demonstrate the system using a portable teletype terminal with an acoustic data coupler and a regular telephone line directly to the

computer.
8. References

1. Jorgensen, Hakon, Distant Identification and

One- finger Registration . Publications of

International Police Conference, Police

Department, New York, 1923.

2. Collins, CoSo, A Telegraphic Code for Fingerprint

Formulae . Scotland Yard, London, 1921.

3o Battley, H. , Single Fingerprints . H.M. Stationery

Office, London, 1930. (p. 10)

4. Ibid

5. Hankley, W.J., and Tou, J.T., "Automatic

Fingerprint Interpretation and Classification

via Contextual Analysis and Topological Coding,"

Pictorial Pattern Recognition . Thompson Book

Company, Washington, D.C. , 1968.
Figure 0.

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13
ABC A B

12 e 7 34

s 3 5

6

7

s 8 78

i 2 8

9

Figure 11

Code for Figure 5 As Entered in

Computer

1

24

6

78

9 i 2 8

s 3 5 e 7 3

s 8 7

Figure 12

Code for F igure 5 As Stored in File

M A B C D N E F G H

1 1 1 1 1 1

2 2 1 2 2 1

3 4 1 3 3 1 4 6 1 4 4

5 7 1 5 5 1 6 8 -1 6 6 1

7 9 -1 7 e 1 5 8 i 2 8 1 8 s 1 9

9 s 3 5 -1 9 e 3 5 10 e 7 3 -1 10 s 3 7 11 s 8 7 1 11 i 3 8 1 12 e 5 7 13 s 6 5

S = 3 14 e 6 8

15 s 7 6 1 16 s 8 5

Figure 13

Tables Used in Comparing

Code for Figure 5 with Code for Figure 10

14
Figure l<i

15
Figure 15

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From ; From

F igure 14 Figure 15

A B C D E F G H

1 1 1 1 2 1 2 1 3 1 3 1 4 1 4 1 5 1 5 1

7 1 7 1 8 1 8 1 9 1 9 1 10 1 10 1 12 1 12 1 13 1 13 1

i 9 1 14

e 1 2 1 e 1 1

s 1 3 1 e 6

s 1 6 1 e 8 1 e 1 9 1 i 9 1 e 2 1 1 e 12

s 2 11 1 e 1 2 1 e 3 3 1 s 1 3 1 e 3 8 1 e 1 9 e 3 9 1 s 2 6 1 e 4 6 1 s 2 11 1 e 8 6 1 e 3 1

s 8 7 1 e 3 3 1

s 8 11 1 e 3 7 1 i 8 12 1 e 3 9 1 e 4 6 1

i 6 13

S = 26 e 8 6 1

s 8 7 1

s 8 11 1 i 8 12 1

Figur e 16

Tables Used in Comparing

Code for Figure 14 with Code for Figure 15

17
Wl

I

W2

"'in^

W3

;erprint '.

W4 W5 W6

Empress ions in Fi

W7 W8 W9 W10 Wll

le

W12 W13 W14

PI 19 6 2 13 -2 5 6 4 8 10 8 7 6

P2 7 17 5 2 8 2 4 6 8 8 4 6 7 6

P3 2 6 17 8 6 6 4 8 6 8 4 5 4 6

P4 2 6 16 6 11 8 4 4 -2 2 8 6 4

Fingerprint ^5 17 8 4 6 24 4 13 7 9 6 12 8 7 12

Impressions pg 2 2 11 7 4 14 10 5 4 1 4 2 3

Against P7 * 6 4 8 5 6 22 3 5 5 4 10 9 5

File p8 8 6 8 10 5 9

6^ 21 6 6 2 6 3 2 P9 2 4 4 6 8 6 6 6 19 4 2 5 5 P10 4 8 10 4 5 2 2 1 9 15 4 7 6 11

Pll 6 12 2 2 10 3 9 2 6 4 17 10 10 12

P12 5 9 7 8 6 1 5 8 4 7 8 18

12

9 8

P13 4 10 4 6 4 8 2 4 2 8 20

8

8

P14 & 6 6 4 7 4 7 2 8 6 10 8 19

Figure 17

Scores Obtained from Comparing 14

Fingerprint Impressions with 14

Different Impressions from the Same

Finger s„ The types include loops , whorls, and double loops

18
Impressions in F ile

W15 W16 W17 W18 W19 W20 W21 W22 W23

Impressions

Searched

Against

File

P15 17 3 6 1 2 7 5 5 5 P16 9 14 2 3 1 3 1 5 1 P17 3 1 14 8 7 8 7 9 9

P18 4 1 10 7 6 8 5 10 10

P19 1 8 6 10 14 9 7 4

P20 4 8 7 5 13 5 7 4

P21 4 2 6 2 6 8 8 8 8

P22 6 4 7 2 7 4 7 15 9

P23 3 14 7 3 9 9 11 14

Figure 18

Scores Obtained in Comparing 9

plain Arch Impressions with 9 Different Impressions from the

Same Fingers.

19
Impressions in Fi le

Wl

W2

W3

W4

W5

W6

W7

W8

W9

W10

Wll

W12

W13

W14

Impressions

Searched

Against

File

PI

P2

323 4 26 30 32 60 42

P3

P4 4 272 66 16 -12 32 16

P5

P6

34 28 336 65 9 48 21

P7

P8

24 40 45 462 30 24 18

P9

P10 16 16 16 6 285 14 55

Pll

P12 54 16 10 72 42 306 80

P13

P14

24 16 16 16 24 64 380

Figure 19

Identification of Seven Individuals

Using Two Fingerprints (Loops and Whorls)

Impressions in File

W15

W16

W17

W18

W19

W20

W21

W22

Impress ions

Searched

Against

File

P15

P16 238 18 6 25

P17

P18

3 98 56 70

P19

P20

1 56 130 63

P21

P22

16 12 24 120

Figure 20

Identification of Four Individuals

Using Two Fingerprints (Plain Arches)

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