<Tr> <Th> Face value </Th> <Td> 1 penny </Td> </Tr> <Tr> <Th> Estimated value </Th> <Td> £ 3--4,000 (mint) </Td> </Tr> <P> The Penny Black was the world's first adhesive postage stamp used in a public postal system . It was first issued in Great Britain on 1 May 1840, but was not valid for use until 6 May . It features a profile of Queen Victoria . </P> <P> In 1837, British postal rates were high, complex and anomalous . To simplify matters, Sir Rowland Hill proposed an adhesive stamp to indicate pre-payment of postage . At the time it was normal for the recipient to pay postage on delivery, charged by the sheet and on distance travelled . By contrast, the Penny Black allowed letters of up to ⁄ ounce (14 grams) to be delivered at a flat rate of one penny, regardless of distance . </P>

What is the oldest stamp in the world