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Who Goes There?

A Facial Recognition Primer


How does Viisage perform its nearly instantaneous feats of facial recognition? The process begins by reducing the variability of the human face to a set of numbers.

Using a mathematical technique called principal components analysis, one can examine a large group of faces and extract the most efficient building blocks required to describe them. It turns out that any human face can be represented as the weighted sum of 128 of these building blocks, known as EigenFaces. With this technique, the essence of a human face can be reduced to just 256 bytes of information.

The recognition process involves comparing the EigenFace weights for two faces using a proprietary algorithm that generates a match score. Different faces will produce a poor match score; images of the same face will produce a good match score.

In systems that require one-to-one comparison (for example, verifying that you are the person pictured on your driver's license or passport), the EigenFace weights of authorized personnel are recorded in a central database. When someone steps before a camera, his or her face is quickly compared to all of the faces in the database to see if it generates a match.

In a one-to-many search, a database is created containing faces of individuals whose presence would warrant action: known terrorists, most-wanted criminals, or missing persons, for example. Cameras, overtly or covertly deployed at strategic locations, capture, in real time, each face in the field of view and compare it with all records in the database.

With the computational power of a standard personal computer, the Viisage technology can complete the entire facial recognition process in as little as one tenth of a second, with a high degree of accuracy. Independent biometric testing has disclosed that the system has a miniscule error rate. --LM

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