|Postcard from a fingerprint|
Hello, I'm John's fingerprint. I've been with him for a long time, since before he was born actually.
John doesn't notice me all that much, but he would if I wasn't there, in fact there are a few people in the world who have no fingerprints at all. Each of John's fingers and thumbs has a unique pattern, and as far as anyone knows, every fingerprint on each human is unique. Collectively, we all help John grip so that he can lift and hold things better.
These days I'm becoming even more useful. I can unlock his phone or laptop, which means that I identify John without mistakes or the forgetfulness that's part of using a password. It's not all roses though. No-one has proven that fingerprints are unique amongst the seven billion or more humans on the planet. It's likely from the way that we are formed in the womb, but even if we aren't unique, the chance of coming across a doppleganger in the huge and growing human population is very small.
But regardless of whether or not John's right forefinger has a unique print, it's the device that takes an image of the print that's important. As is the software that analyses the image. If neither the imaging or the analysis is up to scratch, then his right forefiger may be considered a match for Mary's pinkie, or the ring finger of a farmer in Mongolia.
For fingerprint identification, it's not genetic uniqueness that's the issue, it's whether or not the software that analyses the image is good enough. If that doesn't recognise whorls or islands in sufficient detail, then John's finger print may not be found to be unique.
It's like a photograph. The more out of focus it is, the less detail you can see, and the less you can distinguish between a pair of equally out of focus images.