In 1918, the US Postal Service printed a new postage stamp in patriotic colours of red (albeit carmine red), white and blue.
In the centre was a print of a Curtiss JN-4 ('Jenny') plane, intended to celebrate airmail.
At 24 cents, the stamps were controversial, as standard mail used stamps costing three cents apiece.
So when stamp collector William T Robey bought a whole sheet of 100 for $24 he was showing a degree of commitment to the hobby.
This paid off - all the planes on his sheet were upside-down.
Invert errors typically occur because stamps with complex designs involving more than one colour may require two or more trips through the printing machine.
If a tired worker places the stamps the wrong way round after its initial processing an invert error is produced.
To date, no examples of the Inverted Jenny have been found which did not come from Robey's sheet.
The Jenny has become the most famous stamp in America - featuring in the film 'Brewster's Millions' and even used on The Simpsons to show Homer's stupidity when he discards a set of stamps, complaining 'airplane's upside-down'.
Robey sold his whole sheet for $15,000.
Soon after that it was broken up into one block of eight, six blocks of four and the remaining 68 as singles.
The price at which Inverted Jennies have been sold has varied depending on quality, but the top price for a single was achieved in November 2007 when $977,500 was paid at auction.
Another was sold the following December, and one of the finest came up for auction in August of this year.
One of the blocks of four was bought by collector Bill Gross in 2005 for $2.7m - the record for a US philatelic item - which he later swapped for a Z-Grill to complete his collection of US stamps.
Even though it's not the rarest stamp in the world, as the classic example of an invert error, the 'Jenny' captures the attention of philatelists everywhere.
We currently have a waiting list of clients interested in purchasing one of these famous stamps. Contact us to be added to it.
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