Passports

BBC News has a report about passport controls:

Serious questions have been raised over Britain's border security after a BBC journalist entered the UK twice on fake and stolen passports. Shahida Tulaganova obtained 20 illegal passports - each from an EU country, including the UK - within months. Those in the trade told her to travel via sea or bus, saying port security was less stringent than airports.
[...]
Shahida travelled across Europe to obtain her false documents for her Panorama investigation. They ranged in price from just £250 to more than £1,500. Some were provided within several days, while others took weeks.
She found her first illegal passport dealer in the centre of London - through an advertisement in a Russian language newspaper. The dealer - Henry - provided her with a genuine Czech passport, by getting someone who looked like her to apply for one, using her photo.

Which makes me wonder why they even bother checking passports. There must be some absolute identifier which can ensure that these things don't happen. Fingerprints maybe? Retinas? I'm all for relatively open immigration, but to be viable, both practically and politically, border crossings need to be strictly enforced, and it has to be possible to easily and unequivocally identify immigrants.