Vase with Medusa's Head

Although photogenic drawings made from direct contact with objects constituted Talbot's first success, the impetus for his photographic experiments came from his desire to capture images seen in a camera obscura. This optical device, invented in the seventeenth century and in common use as a draftsman's aid by the eighteenth, consisted of a wooden box fitted with a lens that projected an image that could be traced on thin paper. Frustrated by his lack of facility as a draftsman as he sketched at Lake Como in 1833, Talbot recalled his use of a camera obscura a decade earlier and mused "how charming it would be if it were possible to cause these natural images to imprint themselves durably, and remain fixed upon the paper!"
Sculpture and plaster casts were ideal subjects for Talbot's photographic experiments with the camera obscura; they reflected the sun well and remained motionless during the long exposures required for the lens-projected image to register on the sensitized paper. The camera image thus produced was tonally reversed--it was, in the words of Talbot's colleague Sir John Herschel, a "negative." To make a "positive" image, the negative made in the camera was itself placed in contact with photogenic drawing paper and exposed to sunlight. Although Talbot's process had the potential of producing hundreds of identical prints from a single negative, he printed very few positives of his 1839 and 1840 camera images. This print is thus one of the earliest and rarest of photographs, the tentative beginnings of a process destined to pervade modern life.

[MD; Waking Dream, p. 265]