What is the Most Reliable Biometric Technology?

I was recently asked which biometric technology I thought was most reliable. This is a relatively easy question to answer until I considered the wider issues of using it as a form of identification for access management and then trying to work out which technology is best.

Physical biometric identifiers are the distinctive and measurable characteristics used to identify individuals such as facial recognition, fingerprints, palm vein, iris and retina patterns etc.

The reliability of a technology tends to be the inverse of the social acceptance of that technology. Fingerprints are socially accepted with some resistance from those that associate them with criminal behaviour but they have a relatively high false positive or rejection rate. Which may be fine on a small access control system to a comms room but in an airport with thousands of passengers passing through on an hourly basis, a high percentage failure rate is unacceptable. Facial recognition is quite uncontroversial but equally has relatively high failure rates.

It is generally regarded that eye scans are the most reliable form of biometrics. However, technology such as iris and retina scanning appears to have more social resistance due to its perceived intrusive nature. For this reason iris scanning is now more prevalent than the deeper retina scan. The reliability of iris scanning was born out in a study carried out by the National Physics Laboratory some years ago, where is competed against six other technologies and won with the best false match and rejection ratios.

The problem is compounded by the fact that biometric systems provide”probabilistic results”. It is possible to get variable results due to technical issues and degradation of data, such as fingerprint damage for example. There is also evidence of ethnicity, age, sex and medical conditions affecting rejection rates. Having poorly installed and maintained systems combined with the deployment of biometric technology at airports and other high volume portals without understanding the biology of the population being screened could lead to long queues.

In conclusion, no single biometric trait has been identified as fully stable or distinctive and biometric reading technology should only be deployed with this in mind. False positives and reject rates need to be considered in line with the number and the biology of the users of the system.

Are varifocal lenses zoom lenses?

I recently realised that although I knew that there is a distinct difference between varifocal and manual zoom lenses, I did not know the mechanics of that difference.

When designing a system where a range of fixed lenses is just not suitable, one has to turn to manual zoom lenses to get the best field of view. By manual zoom lenses, I mean as opposed to motorised zoom lenses.

Most “manual zoom” lenses are marketed as varifocal but there is a difference between these and a true manual zoom lens. A verifocal, as the name suggests, shifts its focus with every zoom adjustment. Whereas a true manual zoom lens adjusts the optical array so that the focus is fixed to an acceptable sharpness throughout the zoom range.

One element of the optical array moves either closer together or further apart as the zoom is adjusted another element also adjusts to compensate for the focal shift. A true zoom lens uses between three and five moving groups comprising of up to twenty individual optics.

In a varifocal lens there is no attempt to maintain a sharp focus through mechanical or optical compensation. This produces a cheaper zoom lens with the disadvantage of not being able to maintain a constant focus throughout the zoom range.

In most applications, a varifocal lens will be adjusted and “locked off” at the best setting to provide a permanent fixed field of view. However, in a system where each camera interacts with the next and fine adjustment of the field of view is necessary to get the optimum overlapping views, a manual zoom lens is a far more useful tool.

These applications are probably not encountered often but large high quality systems such as one covering the perimeter of a high security establishment, for example may need fixed focal length lenses that can only be achieved using manual zooms being finely adjusted and then locked in to position. To set up such a system with varifocal lenses would be unnecessarily difficult.

In any CCTV system, the preference from a quality point of view would be to get the survey right, do the calculations and provide a CCTV system with fixed focus lenses.

I would like to thank the members of several groups on LinkedIn for pointing me in the right direction about the mechanical difference between these two types of manually adjusted zoom lenses.