Are Fingerprints Unique?

MattJ writes "There's an incredible article in LinguaFranca about fingerprints. Maybe they're not all unique after all. And maybe those fingerprint experts are not much more scientific than handwriting experts. Fascinating details."

Comments

Well, it's time to do the math....

[ka9dgx]

It's time to push for someone to do the math, some experiments, and determine the actual error rates, factors, etc. I can't believe there is NO possiblity of an error in a "match". There has to be a false-positive as well as a much higher false-negative rate, we need to know what they are, so we, as a society, do the right thing, instead of the emotionally appealing expedient.

To guestimate, I suspect the real numbers are about 10^12:1 false matches, which is quite alarming, if there are 10^7 entries, one in 10,000 will be a false hit with someone totally at random. The false negative rate is probably closer to 1% and might be as high as 10%.

Does anyone have better numbers, after all, I'm just guessing at this point.

--Mike--

Finger Prints

[CakerX]

Well fingerprints although not unique as we once though still provide good evidence. I remeber reading somewere that about 1 in 10,000 people have similar fingerprints. they still would be crucial evidence if the over 100 people with the same fingerprints in the country never set foot in the city.

Well, why not test it?

[Jonathan]

The software is available (in every police station), the data is available (also in the police stations) -- let's just see what the percentage of cases where the programs claim that the figureprints of two different people are the same.

Just had fingerprinting done

[truefluke]

I needed to be fingerprinted before they would give me my green card, what fascinated me was this machine they took my fingerprints on.

At first glance it looks like a photocopier gone haywire, with a largish monitor. This is where your fingerprint image gets projected. There are several squares of different sizes, and they look similar to the glass partition of an everyday photocopier.

No ink involved, He just asked me to lightly place my fingers on the glass, and he held my fingers at some points to keep them from jiggling (he was very exacting about it).

When he was satisfied, he brought the images of my prints up on the screen in front of us. He remarked "Well, no life of crime for you". He was referring to the fact that I had "excellent patterning". He remarked that "You have excellently defined fingertips" etc. etc. He then showed me the neatest thing he magnified my prints to the point that he could COUNT the skin pores between the whorls of my thumbprint

Actually I was impressed, since up til that point it had always involved me getting my fingers full of that stupid ink and having to roll them around on a piece of paper. That machine was much cooler.

And for the record, I don't have one :)

The birthday paradox

[XNormal]

The first person to fashion a statistical foundation for this assumption was the British gentleman scientist Sir Francis Galton. He calculated the probability that any two fingerprints would resemble each other in all particulars as one in sixty-four billion.

Even if you accept this figure of one in 64 billion the birthday paradox predicts that you can expect to find an identical pair of fingerprints in a database of sqrt(64e9) fingerprints which is just a little over 250,000. I believe the FBI fingerprint database is significantly larger than that. After this "threshold" of sqrt(N) is crossed the number of duplicates starts to rise quite sharply as the database size increases.


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