* On 6 November 1914, German officer Carl Lody was executed by firing squad at the Tower of London after being found guilty of spying. He'd travelled to the UK using someone else's American passport, but no suspicions were aroused initially because passports didn't contain any photo identification. Five weeks later, the US Secretary of State ordered the introduction of passport photos. This weekend, 100 years ago, the UK followed suit.
* The replacement of vague written descriptions with photos had been mooted since the 1850s, but it took the threat of espionage to usher them in. The new UK passport was bound in blue cloth with a gold crest and consisted of a sheet of paper with a description of the bearer, the expiry date, some regulations and space for a clipped photo. It quickly became evident that stapled photos weren't tamper-proof; some countries conducted experiments with rivets or glue, instead.
* In his book The Passport, Martin Lloyd describes how the first passport photos would often contain the "imitation waterfalls or plywood balustrades so beloved of the 19th-century photographer". Plenty of people wore hats in their pictures. As a consequence, the first set of British passport photo regulations, issued in 1920, would stipulate 'no hats'.
* In 1940, a Committee of the British Standards Institute laid down some new and excessively detailed regulations. They even specified which film would be suitable (the Barnet, Gevaert and Selo Spool No 20) and the minimum permissible focal length (4in). Shortly afterwards, it was pointed out to the committee that British roll-film cameras only had 3in lenses, so they quietly scrapped these rules. The new ones simply specified a full-face, head-and-shoulders shot, 2in wide, 2in tall. (And still no hats.) (Obviously)