Fixing Fingerprints

March 23, 2010

I can remember being told, when I was a small child, about the shape of snowflakes, and looking at some of them through a simple microscope.  It was something of a revelation that there could be so much structure in something so small.  I also remember being told that no two snowflakes were exactly alike: every one was unique.  It was only a little later that I started to wonder how anyone could know that — surely examining and comparing all the snowflakes in existence was impossible.

In a somewhat similar way, we have all been told repeatedly, in a message that takes many forms, and is regularly reinforced by crime fiction and cop shows on TV, that fingerprints are unique — that the presence of a fingerprint someplace that matches Mr. X is irrefutable proof that Mr. X was there.  It is rare that we ask ourselves why we are so sure.

It should be evident, as a matter of principle, that we really cannot make the statement that fingerprints are unique with any existing, or even imaginable, scientific justification.   That statement is equivalent to saying that there is no pair of fingerprints anywhere at any time that match, a proposition that is impossible to prove.  The best we can hope for is a probabilistic statement about the extremely low likelihood of a match occurring by chance (like the statements that are made with regard to DNA evidence).

As I have noted before, even DNA evidence, generally regarded as the “gold standard” of forensic evidence, is not as soundly based as many experts would like.  An article in New Scientist suggest that fingerprint evidence, despite its common use in criminal cases for about a century, may suffer from even more serious shortcomings.

Since their first use in 1892, fingerprints have formed the heart of many criminal trials. But recently the realization has dawned that two prints deemed a match by an expert may in fact come from two separate people, due to human error, coincidence, low-quality prints or a mixture of all three.

There have been a few high-profile cases in which suspicions, or even convictions, based on fingerprint evidence have later been proved to be unsound (often based on DNA evidence).  Researchers have shown that different fingerprint analysts can come to quite different conclusions on whether given sets of fingerprints do or do not match.  A 2009 report from the National Research Council, published by the National Academies Press, sharply criticized a whole range of practices in the analysis and use of forensic evidence, including fingerprints:

But fingerprint analysts have been slow to acknowledge the problem, and still present matches to courts with no accompanying error rate – a state of affairs that shocked the US National Academy of Sciences (NAS), which presented a report on US forensic science last year.

Fortunately, it appears that some of the criticism is beginning to have a positive impact.  Some serious work is being done to determine realistic expectations for the accuracy of fingerprint analysis.

Last month the US National Institute of Justice commissioned the School of Law at the University of California, Los Angeles, to investigate error rates associated with fingerprint analysis. “Even though we have been using fingerprint evidence in court for almost a hundred years, not nearly enough is known about how often fingerprint examiners might make mistakes, or in what circumstances,” says study leader Jennifer Mnookin.

It is really imperative that this kind of work be done, and the results published.  We are, at least in principle, trying to operate a system of justice, not just trying to see how many people we can convict.

Laptop Earthquake Detectors

March 23, 2010

The LiveScience Web site has an interesting article about a new volunteer effort, called the Quake Catcher Network, that employs ordinary laptop computers to gather data on earthquakes.  The program takes advantage of the fact that many newer laptops have built-in accelerometers, designed to allow the machine’s hard disk to be shut off if the laptop is dropped.  Acceleration is acceleration, of course, and the device, though less sensitive that a seismograph, can detect quakes of about magnitude 4.0 or greater.  The data is captured and transmitted to seismic laboratories at Stanford University and the University of California at Riverside.

One of the difficulties in analyzing earthquakes, as with other geophysical phenomena like weather forecasting, is getting adequate data.  Traditional seismic sensors cost $5,000 – $10,000, and are typically sited on a fairly coarse grid.

Thousands more computers will be necessary before the network could be used to alert outlying areas of incoming earthquakes, but Quake-Catcher already provides data that other methods can’t, said Paul Davis, a UCLA geophysicist who is not involved with the project.

“Traditional seismic stations are 10 to 20 kilometers [6 to 12 miles] apart,” Davis said. “That makes it very difficult to look at fine details, both caused by the earthquake itself as well as by the ground shaking.”

Getting data at a finer resolution would make it possible to analyze the motion of the earthquake in much more detail.  With a large array of inexpensive sensors, it might even be possible to measure the differential effects of shaking on different floors of tall buildings, which could provide valuable clues to how structures can be made more earthquake resistant.

Like the project to use undersea Internet cables to help with tsunami detection, which I wrote about earlier, this is a clever “extra” use of existing technology to gather useful information.

Mozilla Releases Firefox 3.6.2

March 23, 2010

The good folks at the Mozilla organization have released a new version, 3.6.2 of the Firefox Web browser.  This release was originally scheduled for next Tuesday, March 30, but was moved forward because of its security content.   In particular, it incorporates a fix for a Critical heap corruption vulnerability that might be exploited to execute arbitrary code.   Further information, and a summary of this and other changes in this release, are in the Release Notes.

The new version should be available via the built-in update mechanism (main menu: Help / Check for Updates); alternatively, versions for all platforms (Mac OS X, Linux, and Windows), in a wide range of (human) languages can be downloaded here.  Because of the security content of this release, I recommend installing it as soon as you conveniently can.

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