Name of Report and Author: Identification of Accessibility Issues for Visually Impaired Users of Biometric Technologies: Fingerprint Readers by Antoinette Fennell

1. Introduction

As the world becomes progressively more dependent upon technologies for the provision of every day services, designers of these technologies have to meet an ever-increasing list of demands. Machines simultaneously simplify tasks, speed up processing times, increase security and reduce manpower. However, at the same time that systems and services become more automated and sophisticated, accessibility can become compromised.

Here accessibility problems for visually impaired users of a biometric system - the fingerprint reader - are identified and discussed.

The aim of this study was not to evaluate specific fingerprint reader models, but to evaluate particular attributes of the readers and to identify more general issues encountered by visually impaired users when interacting with biometric technologies. This report covers accessibility issues with the device itself and the accompanying software. Three fingerprint readers were used in this study.

1.1. Biometrics

A biometric is a physical or behavioural feature or attribute that can be measured. Examples are wide and varied and include the pattern of lines on the tip of a finger (fingerprints), the pattern of muscles in the iris, the individual sounds and intonations produced when a person is speaking (vocal signature), the individual strokes in a person's written signature, the pattern of veins on the retina, and so on. (Miller 1994; Jain et al. 1997, 2004; Shen and Tan 1999)

Physiological biometrics are based on measurements and data derived from direct measurement of a part of the human body:

Behavioural characteristics are based on an action taken by a person. Behavioural biometrics, in turn, are based on measurements and data derived from an action, and indirectly measured characteristics of the human body:

Other biometrics include DNA, keystroke recognition, grip recognition, ear recognition, odour recognition and gait recognition.

1.2 Biometric Systems

Biometric systems are technologies that record and analyse a biometric attribute (Miller 1994; Jain et al. 1997, 2004). They extract the individual characteristics of this attribute, and compare this data to records in a database.

Biometric systems use biometric data as a means of proving that you are who you claim to be, or as a means of proving without revealing your identity that you have a certain right (e.g. for gaining access to secure information).

The biometric systems that are in most common use are fingerprint readers, iris scanners, facial recognition systems and voice recognition systems.

1.2.1. Fingerprints

Human fingertips are characterised by a series of tiny ridges and valleys on the outer layer of the skin (Shen and Khanna 1997; van der Putte and Keuning 2000). These ridges and valleys form a series of concentric curves and circles, the pattern of which is unique to each individual. A fingerprint is the pattern that is transferred from the tip of the finger. For over one hundred years law enforcement agencies throughout the world have used fingerprints as a means of accurately identifying a person (Lee and Gaesslen 1991).

1.2.1.1. Fingerprint readers

A fingerprint reader uses a sensor to record an image of a fingerprint, which closely resembles the traditional ink fingerprint. How the image is recorded depends on the underlying technology (van der Putte and Keuning 2000).

The first generation of fingerprint readers used optical scanners. Now however, there are a number of different options on the market, using a variety of different internal sensors: optical sensors, ultrasonic sensors, solid state electronic field sensors, solid state capacitive sensors and solid state temperature sensors.

Two of the three fingerprint readers used in this study contained optical scanners. The third contained a capacitive scanner. Optical scanners take a photograph of the ridges and valleys of a fingertip by projecting LED light onto the finger. Whereas capacitive scanners take an image of a fingerprint through means of an electrical current.

With respect to accessibility, the internal technology of the fingerprint reader is not important, but rather the part of the technology with which the individual interacts, and the series of actions and behaviours that the individual must perform to successfully enroll and verify a fingerprint scan (called the 'user interface').

The following is a simplified example of what happens during the two phases of fingerprint registration and fingerprint authentication (Jain et al. 1997):

  1. The process starts with the individual placing a finger on the fingerprint reader.
  2. The reader takes one or more images of the fingerprint. Typically, to ensure accuracy, at least three images will be recorded. This often involves the user removing and replacing the finger between each scan.
  3. The software connected to the reader then compares the multiple images and identifies unique characteristics of the fingerprint. It does so by identifying 'landmark features' (the rapid inflections and terminations) on the print. The features are stored for future identification. The registration (or enrolment) process is now complete.
  4. The authentication stage starts with the individual placing a finger on the reader.
  5. The reader takes an image of the fingerprint.
  6. The software identifies unique landmark features on the print.
  7. The software places the identified landmark features over the landmarks of a previous record of the same print.
  8. A probability value is calculated, which is an estimate of the likelihood that the two prints are from the same finger.
  9. On the basis of this estimate, the fingerprint is rejected or accepted.

The probability value and resulting level of security can be altered depending on the circumstances. In high security situations, such as prisons or government buildings, the probability value (see point 8 above) can be increased to 99%, which means that there is a higher chance of rejecting a person who should actually be accepted (called a false reject).

In relatively lower security situations, such as school attendance, the probability value can be reduced to (for example) 95%. In this case, there will be a higher chance of mistakenly accepting a person who is not actually registered (called a false accept).

1.2.1.2. Problems predicted with fingerprint readers

Using a new or unfamiliar technology for the first time can be a very daunting experience. Members of the general public, in particular those who have not grown up using technology on a daily basis, can find the experience stressful and embarrassing. The protocol is not always self-explanatory and solutions to problems may not be obvious, particularly if the user panics.

The primary aim of this study was to ascertain if visually impaired users of biometric systems encounter difficulties when using the technology. And if so, to identify what these problems are.

Before carrying out any user evaluations, it was possible to predict some general problems that could be encountered by visually impaired users of all technologies. These include that the user may not be able to see where the reader is located; the user may not be able to see, read or understand the instructions; and if the reader is built into a terminal, it may not be distinguishable from the rest of the terminal. Also, the user may not necessarily know how to interact with reader, i.e. which finger to enroll, where and how to place it and for how long to hold it on the reader.

It is important to note that most, if not all, of these predictions could potentially apply to non-disabled users. These predictions provided justification for further investigation into accessibility issues of fingerprint readers.

 

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