© National Museum of Science & Media / Science & Society Picture Library
Salted paper print by William Henry Fox Talbot (1800-1877). Fox Talbot invented the negative/positive proces for producing photographs between 1835- 39. Any number of prints could be made from the same shot by transferring the negative image on to special paper to make a positive print; these prints were called calotypes.
'The Ladder', c 1845.