Fingerprints are composed of friction ridges which a foetus develops in the womb from around 13 weeks onwards. No two fingerprints are alike - not even for identical twins. There are four main defined patterns - arch, tented arch, whorl and loop - and it is the arrangement of these that allows the trained eye (or dedicated software programme) to detect differences and similarities between individual prints.
Even though we constantly shed skin, the fingerprint pattern remains unchanged throughout a person's lifetime. The uniqueness of fingerprints was recognised in Babylon and ancient China, but it wasn't until 1891 that they were used to fight crime. In British colonial India, criminals had to have a rolled fingerprint image on their files. It took another 10 years for the UK's first fingerprint bureau to be established at Scotland Yard.
The first successful conviction based on fingerprint evidence was a burglary case in 1902. Police in the UK hold a database of more than 6 million identified and 700,000 mystery fingerprints.