Hand-scan technology utilizes the distinctive aspects of the hand – in particular, the height and width of the back of the hand and fingers – to verify the identity of individuals. One of the most established biometric technologies, hand-scan has been used for years in thousands of verification deployments. Hand-scan is a more application-specific solution than most biometric technologies, used exclusively for physical access and time and attendance applications.
Components
All components of a hand-scan system – acquisition hardware, matching software, and storage components – reside within a standalone device. Hand-scan systems are capable of storing thousands of user templates in internal memory and can be used in conjunction with cards that store user IDs for template retrieval. Small processors perform the template creation and matching functions, returning responses through a small display panel. Hand-scan systems are normally integrated into existing access control systems, opening doors upon successful authentication, or into time and attendance systems. Hand-scan deployments that includes a large number of doors and employees can be centrally managed, such that enrollment templates from one device can be transmitted to a number of other devices. This prevents users from having to enroll on each device they plan to access.
Data acquisition and processing
In order to enroll or verify in a hand-scan system, users place their right hand on a recessed, covered metal surface. Five pegs ensure that the hand is positioned correctly, with fingers slightly separated and the palm resting flat. A series of cameras acquire 3-D images of the back and sides of the hand. Users are required to place their hand on the device three times in order to enroll and once to verify.
Hand-scan devices are integrated units, with image acquisition and processing functions effectively inseparable. The acquisition process for hand-scan is extremely simple and brief-enrollment of all three hand-scan images can be done within 5 seconds. Verification too, is nearly immediate – once the user’s PIN is entered, verification takes less than 1 second. If users misalign their fingers, LEDs indicate the problem area.
Some users cannot provide sufficient hand-scan data to enroll. Users with very small hands may not be able to reach the guidance pegs or spread their fingers widely.
Distinctive features
Users often mistakenly believe that hand-scan readers use palm prints for verification. While forensic searches can utilize palm prints, hand-scan devices measure approximately 90 different features of the hand and fingers. Distinctive features include overall hand and finger width, height, and length; distances between joints; the hand’s bone structure; and other elements. It overlooks the tips of the fingers, which can vary in appearance as fingernails grow or are cut. Features acquired by hand-scan systems are not highly distinctive, meaning that the technology cannot be used for identification and is not ideally suited for extremely high security implementations.
Template generation
The distinctive features of the hand and fingers are extracted from the series of 3-D images and recorded into a very small 9-byte template (most biometric templates are at least 100 bytes, and many approach, 1000 bytes). The small template size allows many user templates to be stored in a very small amount of memory, but it is also reflective of the relative lack of distinctiveness of hand scan data.
Template Matching
While the hand’s bone structure and joints are fairly stable characteristics, under certain circumstances the appearance of the hand can change enough to cause problems. Swelling of the hands can mask the underlying structure, as can various hand injuries. As in most biometric systems, thresholds can be adjusted to allow for higher or lower levels of security or convenience.
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