The world's first adhesive postage stamp used in a public postal system, the Penny Black, is being celebrated in a Google Doodle on its 175th anniversary.

Featuring a profile of Queen Victoria, the stamp was issued on 1 May 1840 for official use from 6 May that year.

The idea of an adhesive stamp to indicate pre-payment of postage was part of Sir Rowland Hill’s proposal in 1837 to reform the British postal system.

Hill was granted a two-year contact to run the new system after creating a design, finally deciding on an easily-recognisable profile of 15-year-old Princess Victoria, which he believed would be difficult to forge.

Penny Blacks can be highly collectable, with one set of four unused 1840 stamps available on the market for a whopping £140,000, while used versions can still sell for around £870.

Despite these prices, they are not know to collectors to be particularly rare. The total print run of Penny Blacks is believed to have reached 286,700 sheets, or a total of 68,808,000 stamps. The only known complete sheets are owned by the British Postal Museum.