Pam.

Pam, 1944 - MI5 staff member pictured on beach. This ordinary looking snapshot was taken and planted as part of a complex WWII intelligence plan known as Operation Mincemeat.

The intention was that this photograph would make other documents secreted with it seem more authentic. These documents, passed on to German agents after they were found on a body washed up on the coast of Spain (planted by British intelligence) suggested that the Allies were not planning an invasion of southern Europe via Sicily. This led to a weakening of German defence of Sicily which assisted the eventual Allied attack.

Via The National Archives UK's photostream.