Americana postage stamps
Americana postage stamps was a series of stamps released in the United States of America between 1975 and 1981, looking back at the nation's history.
They were designed to celebrate the country's principals of justice and freedom, with typical stamps displaying messages like 'to cast a free ballot - a root of democracy'.
The series itself was made up of 20 stamps issued in sheets, twelve issued in coils and one which was made especially for a booklet.
The stamps were centred around five distinct themes, which were Roots of Democracy, Rights and Freedoms of the American People, Symbols of America, Pioneer America and America's Light.
The most famous stamp in the series is the CIA invert, depicting a lamp to symbolise 'America's Light Fueled by Truth and Reason'.
Its face value was $1, but because of the error, and the rare nature of stamp as only 100 now exist, it is valued much more highly by philatelists. It is now valued at $15,000, and a block of four stamps sold for $60,000 in 2004.
This value is nothing compared to that of arguably the most sought after stamp in the world, the Inverted Jenny. Original stamps from the 100 that were printed have sold for as much as $977,500.
Printed on May 18, 1918, it shows an upside-down biplane flying through the air.
Stamps by country
Great Britain was the first country to issue a pre-paid postage stamp on May 1 1840, followed by the Canton of Zurich in Switzerland, and then Brazil. Since then stamps have been issued by the majority of countries worldwide. The European country of San Marino lists postage stamps as it's most valuable export.
A stamp dealer is a person or business that trades in postage stamps. Dealers often specialise in certain areas, from themes such as chess on stamps, to countries or historical periods.
In the United Kingdom the Philatelic Traders' Society issues a code of ethics for stamp dealers to abide by.