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IR Imaging Is Key to Biometric ID

Photonics Spectra
Jul 2002
Brent D. Johnson

Biometrics uses data processing to identify an individual by a unique biological characteristic; e.g., by a digitized fingerprint or iris pattern. It provides important tools for preventing or limiting such criminal activities as credit card fraud (identity theft), unauthorized cell phone usage, unsanctioned access to secure locations and falsification of immigration documents. Interest in biometrics has increased with the emphasis on security following the events of Sept. 11.


Infrared mapping of a subject's fingertip provides thermal emissions data that can be compared with a control image for positive identification in seconds.

A patented thermal mapping technique developed by PosID Inc. overcomes limitations of existing biometric methods, including the possibility of manipulation and dependence on constant atmospherics such as background lighting. The technology is remarkably straightforward. The human body is an efficient emitter of long-wavelength infrared, often referred to as thermal radiation. Because skin is reasonably transparent at wavelengths around 7 to 8 µm, an image of it taken at this wavelength is not homogeneous, but contains spatial details that depend on local variations in the thermal emission properties of the underlying tissue (blood vessels, muscles and fat deposits). Moreover, in comparisons of some 22,500 images, the company has shown that each emission pattern is unique not only to an individual, but also to a particular finger -- or thumb -- tip.

PosID has built a portable reader/recognition system whose critical components are the proprietary pattern-recognition process and matching software, and a long-wavelength Merlin camera from Indigo Systems Inc. The camera uses a 320 x 240 microbolometer array and filters optimized for 7- to 8-µm detection.

Thomas Ball, director of business development at PosID, said his company selected the Merlin camera because it provides high-resolution imaging and ease of use. It delivers low-noise, real-time images at up to 60 fps with low power consumption. In addition, it could be integrated into the system without requiring external cooling or special hardware.

In the Thermo-ID identification process, the camera's optics are focused on a contact window where the subject places a fingertip. The raw image goes through manipulation and analysis, including smoothing and automatic centering (registration), followed by pattern recognition routines based on military target analysis techniques.

Ball said that the technique has a number of advantages over other biometric methods. It is nonintrusive and requires minimal user effort, no user skill and no external illumination source; it also is highly accurate. The company, he added, has evaluated the statistical performance of the prototype using the same testing protocols employed by the Fingerprint Verification Competition (FVC2000), a method prescribed by the National Biometric Test Center in San Jose, Calif. The thermal imaging prototype's performance curves exceed those of the best-performing algorithms of the FVC2000. It makes positive identification (or rejection) in less than three seconds. And, the biometric identity is permanently physically associated with the individual and cannot be stolen or borrowed.

The developers envision many potential applications for the technology. For example, at ATMs, it would allow simple verification of the user by comparing an acquired image with image data stored directly on the card. Or it could be used to provide selective secure access at permanent sites or in a temporary location, such as a crime scene or disaster area.

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