Exploratory study on classification and individualisationof earprints

Lynn Meijermana, Sarah Shollb, Francesca De Contic, Marta Giaconc,Cor van der Lugtd, Andrea Drusinic, Peter Vanezisb, George Maata,*

aBarge’s Anthropologica, Leiden University Medical Centre, P.O. Box 9602, 2300 RC Leiden, The NetherlandsbDepartment of Forensic Medicine and Science, University of Glasgow, Glasgow G12 8QQ, UK

cDepartment of Biology, University of Padova, Via V. Bassi 58B, 35131 Padova, ItalydInstitute for Criminal Investigation and Crime Science (LSOP-ICR), P.O. Box 9016, 7200 GT Zutphen, The Netherlands

Received 16 April 2003; received in revised form 20 October 2003; accepted 27 October 2003

Abstract

The FearID research project is aimed at the individualisation of earprints for the purpose of forensic research. The study

presented here was carried out within the framework of this project. It intends to combine a review of what is known from

literature on the classification and individualisation of earprints with results from a preliminary study of earprints. Possibilities

for, and limitations to, the use of earprints in forensic investigation are addressed. Differences between eliminating a suspect,

placing a suspect at a crime scene, and linking crimes by prints left at different scenes are considered.

# 2003 Elsevier Ireland Ltd. All rights reserved.

Keywords: Earprint; Identification; Individualisation; Classification; Crime scene mark

1. Introduction

When a burglar listens at, for instance, a door or window

before breaking and entering, oils and waxes on the ear leave

a print that can be made visible using techniques similar to

those used when lifting fingerprints. The ‘FearID’ research

project, a collaboration of several European institutes, is

aimed at the individualisation of such an earprint to a person.

The study presented here was compiled within the frame-

work of this project.

An earprint is a two-dimensional reproduction of the parts

of the auricle that touched a surface, like the print of a rubber

stamp. Unlike the regular print surfaces on a stamp, the

elevation and the flexibility of the various morphological

structures of the auricle vary. Some structures will therefore

leave an imprint, while others may not, or do so only partly.

This will depend on the position and elevation of each

morphological structure in relation to the position and

elevation of the other structures. Also, the amount of oil

that is naturally present on the various parts of the auricle

may play a role. Absence of a feature in a print may therefore

be informative of both the condition of the listener and the

morphology of the live ear.

Features most frequently found in earprints are imprints

of the helix, anthelix, tragus and antitragus (see Fig. 1). The

latter two may be a continuation of the outline of the

intertragic notch, but may also appear as two separate

patches. The imprints of anthelix and antitragus are also

often connected, and sometimes this may be the case for the

imprints of anthelix and helix too. Furthermore, the imprint

of one morphological structure may be broken up into one or

more separate patches. This is particularly the case for the

imprint of the helix. Features that may also be found in

earprints include imprints of the earlobe (part of) the crus

helicis, and the crus superior anthelicis and/or crus inferior

anthelicis. A crus posterior anthelicis is relatively rare in the

actual ear [1], and its imprint therefore occurs less com-

monly in earprints. The imprint of a crus cymbae, not being a

common structure in the actual ear [2,3], is even less likely to

be found in an earprint because of its low elevation. Part of

Forensic Science International 140 (2004) 91–99

* Corresponding author. Tel.: þ31-71-5276647;

fax: þ31-71-5276680.

E-mail address: g.j.r.maat@lumc.nl (G. Maat).

0379-0738/$ – see front matter # 2003 Elsevier Ireland Ltd. All rights reserved.

doi:10.1016/j.forsciint.2003.10.024

Fig. 1. Examples of earprints, showing inter-individual variation and indicating some characteristic features (features are not necessarily marked

in all prints). Compiled using illustrations from van der Lugt [18]). (1) Crus helicis (anterior section), (2) crus helicis (posterior section), (3) helix,

(4) characteristic notch in inner rim of helix, (5) interruption of helix, (6) Darwinian nodule, (7) Darwinian enlargement, (8) knob on superior part

of helix, (9) anthelix (body of), (10) crus anterior anthelicis, (11) crus superior anthelicis, (12) crus posterior anthelicis, (13) inferior extension of

anthelix, (14) appendix of anthelix, (15) characteristic constriction of anthelix, (16) Tragus, (17) anterior knob of tragus, (18) anterior notch, (19)

antitragus, (20) intertragic notch, (21) posterior auricular furrow, (22) scapha, (23) earlobe, (24) crease in earlobe, (25) pre-auricular area, (26)

creases in pre-auricular area, (27) pre-auricular sinus, (28) skin detail indicating baldness, (29) apex of scapha.

92 L. Meijerman et al. / Forensic Science International 140 (2004) 91–99

the pre-auricular region is, however, often represented in a

print, and seems to provide valuable information due to

characteristic creases of the skin in this area.

Hirschi [4,5] was among the first to recognize the value of

earprints for forensic identification. Ever since, several

studies have been presented, acknowledging the feasibility

of using earprints for this purpose [6–13]. Some basic

questions, however, need to be addressed. How unique is

the human ear, and how stable are its features? Moreover,

how unique is the earprint? Can one ear make prints that vary

substantially, and can two different ears create similar ear-

prints? Knowledge of both variation between several prints

made by a single ear (intra-individual variation) and varia-

tion that occurs between prints that each have been made by

a different ear (inter-individual variation) is of great impor-

tance [14]. Uniqueness of the human ear will be difficult, if

not impossible, to establish. To justify the claim that we can

match an earprint uniquely to an ear, we must establish that

the print resembles other prints from the same ear more than

it resembles prints from another ear. We may attempt to do so

by analysing multiple prints from a large sample of ears,

comparing inter-individual variation with intra-individual

variation over a suitable set of measurable features. An

experimental feature set is suitable only if the inter-indivi-

dual variation is significantly greater than the intra-indivi-

dual variation. For such a comparison, we may use, for

instance, cluster analysis or formal concept analysis

(Ingleby, personal communication). The outcome of this

analysis will be probabilistic. This means we may estimate

the probability of encountering seemingly indistinguishable

prints from different ears. Until now, no such statistical

analysis has been performed. It is, however, part of the work

that the FearID team hopes to accomplish.

An extensive classification of the various features in an

earprint will aid in determining the extent of inter- and intra-

individual variation, and will provide the tools for a statis-

tical analysis. With this study, we aimed to combine a review

of what is known from literature on the subject of classifica-

tion and individualisation of earprints, with results of a

preliminary study of earprints that we have carried out

ourselves.

2. Use of prints in forensic research

Earprints in forensic research can be used for various

purposes. Firstly, a latent earprint found on a scene of crime

may be used to exclude a person as a possible suspect, as

indeed Scaillet [12] excluded one of two possible accom-

plices of two criminals who had confessed to a series of

offences. When utilizing earprints only to dismiss a suspect,

using transparency overlays to establish the degree of simi-

larity will often quickly reveal that a person was not respon-

sible for leaving a latent earprint. Establishing that two

different ears will not make similar earprints is no prere-

quisite when prints are used in this manner. We do, however,

need to be sure that various prints made by one ear do not

vary to the extent that we would not recognise these prints as

being created by a single ear.

Besides eliminating possible subjects from further inves-

tigation, one may also use the latent earprint to increase

evidence against a given suspect, as Scaillet [12] did for the

other of the two possible accomplices mentioned above.

Other examples of this use for earprints are Dubois [6] and

Hirschi [4]. In order to do so, one also has to have a control

print of a possible suspect already at one’s disposal, and the

transparency overlay technique will again quickly reveal the

degree of similarity between the latent earprint and the

control print. Assuming that the latent earprint and the

control print are a (more or less) perfect match, we must

establish that the probability of two similar prints being

made by two different ears is sufficiently close to zero in

order for the latent print to be accepted as evidence.

A third method of using earprints in forensic research may

be applied when there is no suspect available. A latent print

may then be compared to a database containing prints

recovered from crime scenes, each of them linked to a case,

or possibly even a perpetrator through other forms of

evidence or a confession. A database could also contain

control prints taken from large groups of people, or a

combination of both. When using earprints to link cases

this way, it is not sufficient to know that one ear will not

make substantially different prints, and that the chance of

two ears making indistinguishable prints is acceptably small.

We also need to know that, during a certain period of time,

the auricle itself usually does not change to the extent that it

would be impossible to locate a print from the same indi-

vidual at a different age in a database. Depending on how

accurately we need to process the exact dimensions of the

print in order to find an acceptable number of possible

matches, it may be possible that a print in the database is

not found as a possible match anymore after a certain period

of time. This would not mean, however, that another person

risks to be incriminated, since dimensions are merely used

for initial classification and weak linkage, while individua-

lisation will most probably depend on the presence and

position of minutiae, e.g. creases, papules or other details

of the skin, and characteristic notches or angles in the outline

of imprinted features.

3. Variability and stability of the auricle

When addressing the uniqueness of the auricle itself, the

snowflake paradigm—frequently voiced as ‘‘nature never

repeats itself’’—has been applied for forensic purposes [15].

In several publications on the variability of ears and/or

earprints [16–18] and case studies of police investigations

[4,8,19], it was assumed that no two ears are exactly alike.

The assumption was based merely on the absence of two

indistinguishable ears in conducted surveys; the individual-

ity of human ears has never been empirically established

L. Meijerman et al. / Forensic Science International 140 (2004) 91–99 93

[20]. However, as Hoogstrate et al. [21] have stated, avail-

able studies do suggest that the variability between ears is

that large that it might be possible that ears are uniquely

distinct on a limited number of features or characteristics.

Although variability in the morphology of the actual (live)

ears of different people does not automatically lead to a

similar variability in their prints, it may nonetheless be very

informative to study this variation in morphology. It will

assist the interpretation of features in a print, and it will

facilitate the distinction between inter-individual and intra-

individual variation. An indication of the frequency at which

certain morphological structures, such as a Darwinian

nodule or a (pre)auricular sinus, occur in various ears will

further provide information on the value of their imprints for

identification. It is, however, by no means necessary to try to

‘recreate’ a three-dimensional structure from the two-

dimensional print in our minds, in order to be able to

individualise a print, as we can compare prints with prints

and not with the auricle itself.

For a latent earprint to be useful as a means of identifica-

tion, not only the variability between ears (and therefore

earprints) must be sufficient, but the ear (and its prints) must

be relatively stable as well. The auricle, however, does not

remain unchanged throughout life. Some features may be

changed intentionally through piercing; others may change

through disease, or by scarring or other trauma. Provided the

changes are not too extreme, they will not alter the basic

dimensions and characteristics (and therefore diagnostic

features) of the auricle. Once recognised, they may even

make the ears positively more distinguishable from others.

In addition to such relatively sudden changes, the auricle

increases in dimensions due to growth [2,22–24]. Although

this might affect the chance of finding a print in a database

after a long period of time, it is unlikely to make the ear less

‘unique’. Also, natural changes in the auricle (such as

resulting from growth) develop slowly and are small, espe-

cially when considering the time-span we are dealing with in

forensic practice. Here, this is not ‘a lifetime’ but, at most,

the time that passes during which legal prosecution is

possible. Still, a study of the growth of the auricle should

be part of a comprehensive study on ears and earprints, and

the issue will therefore be dealt with in a separate study.

4. Intra-individual variability in prints

Changes in the auricle are not the only possible source for

intra-individual variation in earprints; differences in the way

prints are left, or the material they are left on, may also cause

variation in prints by a single ear. Due to variation in

elevation and flexibility of the various structures of the

auricle, not all features in the prints are created simulta-

neously, nor are they affected in a similar way by changing

pressure. Consequently, the amount of force that is applied to

the surface by the ear during listening may significantly

influence the appearance of the resulting print. Neubert [25]

compared the dimensions of features in a print directly to

dimensions of the auricle. He did so for prints that were

taken at two levels of applied force (‘soft’ and ‘hard’) of both

ears of fifty subjects, and found that length and width of the

auricle usually exceeded the corresponding dimensions of

the unstressed auricle and increased as more force was

applied. He further noted that length increased more (and

more often) than width, that the imprint of the upper part of

the helix differed more from the actual helix than the imprint

of its lower part, and that the minimal width of the imprint of

the anthelix conformed more to the actual minimal width in

the auricle than did the maximal width. The greatest devia-

tion from the unstressed auricle was in the imprint of the

earlobe. The deviation in width was greater than the devia-

tion in length in this feature.

When using prints in forensic research, we need to

familiarize ourselves with the variation between prints made

with various forces, rather than between the morphological

structure and its imprint (although the latter can give some

indication of the former). Saddler [26] studied the influence

of changes in applied force on the various features in a print.

He measured ear length, ear width, anthelix width, and upper

helix width in 92 sets of prints (by 46 left and 46 right ears).

Each set consisted of one print made with ‘soft pressure’ and

one print made with ‘hard pressure’. Width of the imprint of

the anthelix in particular varied with a change in applied

force. In most cases (79% of left-earprints; 70% of right-

earprints), increased force led to an increase in width. In

some prints, however, the width of the imprint of the anthelix

decreased when more force was applied. The total length on

the ear also increased in most prints (in 70% of left-earprints

and 74% of right-earprints). Saddler provided ranges for the

increase in millimetres of ear length (1–6.5 mm) and anthe-

lix width (0.5–5 mm). No specification was, however, given

for the amount of force that was applied, and there was no

indication that the variation in applied force was similar to

variation under natural conditions. Hence, there is no indi-

cation that the variation in dimensions of features in prints he

found during his study would occur in latent (crime scene)

prints by a single ear. Regarding the other dimensions

included in his study, Saddler found that in the majority

of the sets of prints (73% of left-earprints; 60% of right-

earprints), an increase in width of the upper helix could be

observed with increased force. Ear width increased in 47%

of left-earprints and 53% of right-earprints; the remaining

prints showed either no marked difference, or a decrease,

with increased force. Saddler concluded that most dimen-

sions increase with increasing force, but that the imprints of

some structures may change in an unpredictable way.

According to him, this would make searching a database

using metrical characteristics ineffective.

Ingleby et al. [27] tried to avoid the problem of variation

in dimensions due to variation in applied force, by measuring

distances between features in prints while using the intensity

medians lying between the outlines of these features. They

assumed that, as force increases, the edges tend to spread but

94 L. Meijerman et al. / Forensic Science International 140 (2004) 91–99

the intensity medians will remain more or less at the same

position. Dubois [6] came to a similar conclusion when

studying pressure points of an ear that was pressed to a glass

plate.

We carried out a preliminary study of earprints that were

made when subjects were listening naturally at a surface.

Each subject listened a number of times. During each of the

listening efforts, the amount of force applied to the surface

was measured. The resulting prints were dusted using fine

aluminium powder, and preserved on black gel lifters. For

each of thirty different ears, we copied three to five prints

onto transparency sheets to reveal the degree of similarity.

We also compared digitised prints on the computer by

superimposing them onto each other. This preliminary study

has led us to believe that, in addition to the dimensions of the

separate features, the position of these features to each other

may also change when applied force is varied. This may be

the result of flattening of the entire auricle with higher force,

increasing distances between the estimated centre-points or

centre-lines (‘core-lines’) of most features. We believe that

the arrangement of features in a print may further change

with higher force as a result of a different reaction to

increased force by the upper and lower parts of the auricle,

due to a difference in flexibility of these parts. In Fig. 2, a

digitised print, of which colours were inverted, was super-

imposed onto a different print by the same ear. Areas

appearing black are unique to one print, and areas appearing

white are unique to the other. When the antero-superior parts

of the helix and anthelix in both prints are matched onto each

other, the areas that represent the tragus and antitragus in

both prints do not match.

With respect to the dimensions of the separate features, it

appeared that, in line with Saddler’s findings, these do not

necessarily increase with increased force. For instance, one

print had a very prominent representation of the helix, but

only a very small representation of the anthelix. In another

print by the same ear, made while more force was applied to

the surface, the dimensions of the anthelix had increased, yet

the dimensions of the helix had decreased. Presumably, this

is due to a change in pressure distribution. We further came

to believe that equal variation in applied force does not

necessarily lead to equal intra-individual variation in the

prints. For some ears, small changes in force appeared to

have a relatively great effect on the prints, while for other

ears relative large changes in force seemed to have little

effect on the appearance of the prints.

Our preliminary results confirmed the presence of intra-

individual variation in prints resulting from actual listening

efforts. In order to recognize the limits to realistic intra-

individual variation in prints, we should familiarize our-

selves with the various sources for variation. We suspect that

a necessity for functional listening will limit a person’s force

range, and consequently the variation in prints due to

changes in applied force. The concept of a personal func-

tional force range, determined by the individual morphology

of one’s ear, as well as the extent of this hypothetical range,

will be explored. Certain factors, such as for instance the

amplitude of the target sound or perhaps the level of ambient

noise, may possibly affect force applied to the surface. A

study of the effect of various factors on applied force while

listening has therefore been carried out within the frame-

work of the FearID project, and will be addressed separately

from this review.

Another source of intra-individual variation may be the

way in which the head is positioned when listening, as the

direction of the applied forces as well as its magnitude may

influence the appearance of the earprint. Handel [28] further

pointed out that latent earprints may sometimes have been

created coincidentally while hiding away, and not while

listening. These prints may result from forces outside a

functional range for listening, and may therefore be distorted

compared to prints made by the same ear during listening.

Other factors besides variation in applied force may cause

intra-individual variation in earprints. One factor is the

quality of the surface that the ear is pressed against. Apart

from a possible effect on functional force as was hypothe-

sized above, it may have a direct effect by introducing a

pattern to the print that is not created by the ear itself.

Saddler [26], for instance, noted that brush strokes on a

painted surface may reduce skin detail in a print lifted from a

painted wooden door. The amount of details to be recovered

from a latent print may also be influenced by the medium

Fig. 2. Intra-individual variation in earprints. One digitised print

(inverted colours) superimposed onto another print by the same ear

(regular colours); black areas are unique to one print; white areas

are unique to the other.

L. Meijerman et al. / Forensic Science International 140 (2004) 91–99 95

that is used to lift the print. Within the scope of the FearID

project, various media will therefore be tested on their ability

to preserve details.

5. Inter-individual variation: classifying variation

and finding diagnostic features

Various studies have focussed on identifying and classi-

fying variation in prints [18,27,29]. Both metrical and non-

metrical systems, or combinations of the two, were proposed

for the classification of the various phenomena. Ingleby et al.

[27] and Maat [29] proposed methods for a quantitative

classification. Both appointed two fixed landmarks and

connected these two in order to construct a polar axis for

geometrical standardisation. They then calculated distances

and angles between structures. Maat [29] chose the common

tangent to the inner edge of the impression of the supero-

anterior curve of the helix and the tip of the tragus to create a

polar axis for geometrical standardisation (Fig. 3). He

proposed to measure distances between an origin at the

tragus and the tangent point of the antitragus, and various

points on the helix and anthelix (Fig. 3: O–A, O–B, O–C, O–

D, O–E, A–B, A–C, B–C). The intersection of lines meeting

the polar axis at two different (fixed) angles and the central

lines (‘core-lines’) of the helix and anthelix determined the

position of the various points on the latter two features.

Central lines were chosen in order to reduce variation due to

changes in width of these features resulting from changes in

applied force. In addition to the various length measure-

ments, Maat proposed to measure five angles: ffOAB, ABC,

OBC, OCA and CAO.

Ingleby et al. let their computer calculate ‘centroids’

(intensity centres) of the tragus and antitragus as, according

to them, the placing of Maat’s common tangent was difficult

to reproduce, and centroid calculation is direct and uncon-

troversial1. Like Maat, Ingleby et al. proposed a number of

length measurements and angle measurements for their

classification. They, however, chose a polar axis joining

the centroids of the tragus and antitragus, assuming that

the imprints of these two morphological structures are

usually present in a print, and expecting that the relative

position of their imprints would be stable because the

structures are the more rigid parts of the auricle. Their

length measurements included the distance between the

centroids of the tragus and antitragus, and between the

centroid of the tragus and three points on the anthelix

and helix.

As mentioned in the previous section, during our pre-

liminary research it appeared that the imprints of morpho-

logical structures do not only broaden due to an increase in

force, but features may change position in relation to each

other as well. A change in position seemed, in fact, to be

frequently the case for the position of the superior part of the

print (including the imprint of the upper part of the helix), as

compared with the position of the antero-inferior part

(including the imprint of the tragus). This is probably due

to the difference in flexibility of both sections of the auricle.

The change in position would affect the direction of the polar

axis as suggested by Maat [29]. The distances between the

polar axis as proposed by Ingleby et al. [27] and the anthelix

and superior parts of the helix would be affected as well.

Additionally, the width of the intertragic notch may change

with increased force, changing the positions of the tragus

and antitragus, and consequently the direction of the

suggested polar axe. Therefore, depending on the existing

intra-individual variation, the suggested methods of initial

Fig. 3. Reference points for metrical characteristics (‘cues’) of an

earprint (Maat [29]). Polar axis: common tangent to inner edge of

the impression of the (onset of the) crus of helix and the tip of

tragus. (A) Intersection of the 2908 line from tragus tip O with the

median line of the anthelix impression, (B) tangent point on the tip

of the antitragus of a perpendicular from the polar axis, (C) tangent

point of tip of polar axis with the median line of the (onset of the)

crus of helix impression, (D) intersection point of the line

extending OA with the median line of the outer helix impression,

(E) intersection point of the 3458 line from tragus tip O with the

median line of the upper helix impression, (O) tangent point of

polar axis with the tip of tragus.

1 In centroid calculation, X- and Y-axes picked arbitrarily. Pixels

(defining a structure) are present in a region of a digitised print at

locations (Xi, Yi), the ith pixel having an intensity or weight Wi. If

W is the sum of all the weights in the region, W ¼P

Wi, then the

coordinates of the region centroid will be (X-bar, Y-bar), obtainable

by calculating weighted sumsP

ðWi � XiÞ andP

ðWi � YiÞ(Ingleby, personal communication).

96 L. Meijerman et al. / Forensic Science International 140 (2004) 91–99

classification may introduce unnecessary deviation. In order

to reduce this problem we propose that, when metrical

characteristics (‘cues’) are used for classification, it is better

not to use those related to a polar axis. One can instead

compare the spatial positions of features to each other. One

may for instance measure the shortest distance between

landmarks, or compare the curvature of (parts of) the helix

and anthelix. To reduce the risk of misclassification, one may

choose to only compare neighbouring structures, or neigh-

bouring parts of structures. Intra-individual variation in the

dimensions of, and distances between, features should be

studied in prints made during true efforts of listening.

Examples of non-metrical characteristics, used when

comparing or classifying prints, are the outline of the

imprints of the various morphological structures, and the

appearance, size, and position of minutiae. Two approaches

have been followed in this qualitative approach. One is to

compare the features in a print with the outline of morpho-

logical structures of the auricle when pressed to a glass plate

[19,30]. The other approach is to compare prints with prints

[18,26,29]. Maat [29] suggested recording the presence or

absence, and position, size and form, of a Darwinian nodule,

and the presence or absence of impressions of the tragus,

antitragus and earlobe. He further included recording the

position, size and form of papules and scars, the position and

pattern of creases of the pre-auricular area, anthelix and

helix, and the pattern of hair-related hillocks and dimples of

the anthelix, helix and pre-auricular area. Finally, Maat

suggested classifying the appearance of the imprint of the

anthelix according to the presence of extensions from its

body. His classification of the anthelix was copied by van der

Lugt [18]. Maat divided the imprints of the anthelix into

eight categories, allowing for the possibility of a non-clas-

sifiable imprint (Fig. 4). As Maat’s classification was not

meant to describe the live ear, the use of ‘anterior’ and

‘inferior’ for the classification of the anthelix extensions in a

print should not be confused with the names of the actual

crura anthelicis. The presence of an inferior extension in the

imprint of the anthelix may have resulted from a concave

anthelix body (creating a void between the edges), or from a

knob situated at the origin of the inferior and superior crura.

One may even imagine that the imprint of a crus cymbae may

possibly lead to an inferior extension of the imprint of the

anthelix.

Maat based his categories of classification of the imprint

of the anthelix on a database of actual crime scene prints.

One may envisage that further combinations should be

included to cover possibilities that were not yet present in

this database, but could, in theory, be found. A superior-

posterior combination could be one category that may very

well be found in latent earprints, as well as a superior-

anterior-posterior combination. In fact, the illustration of

choice no. 6 in Maat’s classification would have better

illustrated this last category, as the ‘inferior’ part of the

imprint is merely a convex connection between the basal

and anterior part. This illustrates the need to define the

Fig. 4. Classification of the anthelix extensions in a print (from Maat [29]). (1) Superior, (2) anterior, (3) anterior, inferior, (4) superior,

anterior, inferior, (5) superior, anterior, (6) superior, anterior (inferior), posterior, (7) lumping, (8) non-classifiable.

L. Meijerman et al. / Forensic Science International 140 (2004) 91–99 97

boundaries between categories in a classification accurately.

It may further be useful to record which is the strongest of

the extensions, if one is clearly more prominent than the

other(s). The stronger extension will less likely be absent in

prints created with less force than the weaker extension. We

hope to gain a more extensive knowledge on the variability

of each of the various features of a print during the FearID

project. Ideally, we will be able to determine which are the

stable characteristics, and group the less stable ones in such a

manner that, by default, no realistic possibilities are

excluded while classifying prints to search for a matching

print in a database. For any classification scheme of gross

features in a print, achieving inter-subjectivity will be a

challenge. We hope to eventually be able to rely on auto-

mated image-processing techniques for gross feature extrac-

tion through boundary extraction algorithms. This will

decrease the role of the examiner’s perception during the

initial classification.

Not all studies of intra-individual variation in earprints

have used a classification of features, nor may all variation

be easily classified. Iannarelli [16] advised using an overlay

technique for comparing earprints. He further described a

second technique, during which the control print and latent

print are each cut into quarters, and matched together to find

the degree of matching. This technique was adopted by

Kennerley [8] and van der Lugt [18] but might be considered

an unnecessary addition to the overlay technique, only

reducing the possible points of comparison.

As we may expect some variation in the dimensions of the

separate features in different prints of one ear, as well as in

their relative positions, it is likely that the final individua-

lisation of an earprint will greatly depend on physical

minutiae from skin structure. Examples of such minutiae

may be the position, size and/or pattern of creases, papules,

scars, moles, hillocks and dimples, and characteristic

notches along the inner rim of the helix. Comparing different

prints made by the same ear has led us to suspect that

particularly the inner rim of the superior part of the helix

may prove to be very stable, as well as very characteristic.

6. Concluding remarks

Measurements may be hard to reproduce, and classifica-

tions may be subjective. Still, an extensive classification of

features in a print will provide us a tool in order to estimate

the probability of encountering seemingly indistinguishable

prints from different ears. This estimation of false positive

probability will allow us to establish whether or not, and to

what extent, we may use latent earprints in forensic research.

A next phase may then possibly include using earprints for

identification. An (initial) classification of the features in the

latent print will now also facilitate the search for a matching

print in a database. A proper classification of features will

also help in indicating the position of minutiae. It will further

assist interpretation, as imprints of morphological structures

may lump together, or the imprint of a single structure may

appear as separate patches.

Solid knowledge on the variability of earprints left by a

single ear is of great importance during both phases. It will

allow us to record, store and analyse earprints in such a way

that the maximum amount of ‘natural’ variation is taken into

account, without introducing unrealistic variation in prints of

one ear. The latter would likely impede the search for

diagnostic features. Knowing the extent of intra-individual

variability, and recognizing stable features, will aid the

design of a classification system capable of distinguishing

between intra-individual and inter-individual variability.

Acknowledgements

This work was carried out within the framework of the

FearID research project, which was funded by the European

Union. This research project is a collaboration between the

Institute for Criminal Investigation and Crime Science (Zut-

phen, The Netherlands), the National Training Centre for

Scientific Support to Crime Investigation (Durham, UK), the

University of Padova (Italy), the University of Glasgow

(UK), Leiden University Medical Centre (The Netherlands),

The Netherlands Organisation for Applied Scientific

Research (Delft, The Netherlands), the University of Hud-

dersfield (UK), The Netherlands Forensic Institute (Rijs-

wijk, The Netherlands) and NFGD Software Solutions,

Zoetermeer, The Netherlands). The photographs used to

compile Fig. 1 were made by Cor van der Lugt. Jan Lens

drew Figs. 3 and 4. We wish to thank Dr. M. Ingleby for his

helpful remarks and clarification of centroid calculation, as

well as corrections of English text, and Dr. H. de Jong for

critically reading a first draft of the manuscript. We are

further grateful to Ruud van Basten for dusting and lifting

the earprints used during our preliminary research. Two

anonymous referees are thanked for their valuable com-

ments.

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