As the challenges to international security increase, people have looked to biometrics - the capturing of an individuals unique biological data - to provide more reliable evidence of identity. This autumn a new standard will be applied to the machine-readable travel documents carried by an estimated 550m international air passengers a year - and biometric data will be at its heart. So why has the International Civil Aviation Organisation opted for facial imaging as the basis for its new specification, rather than images of fingerprints or irises? ICAOs Mary McMunn explains all to Jonathon Inskip, Head of Business Development at De La Rue.