Like many British postal entities, Gibraltar used the Machin head on its stamps.
This is a stamp from a four stamp series, issued 1979 for the centenary of the death of Rowland Hill. The portrait, of a young and vigorous reformer, would be used on a British stamp in 1995 too.
On this red 9 pence, the stamp depicted is a definitive one of 1971. Yvert et Tellier catalogue gave a precision: it was sold by machines inside a roll of five: two half-pennies, two of this blue penny and one two-pence. And it bears the royal profile that became as famous as the Rock of Gibraltar profile stamp of 1969.