The photogenic drawing, a negative obtained by laying the leaf on light-sensitive paper and exposing it to the sun, has been attributed to Henry Fox Talbot, one of the pioneers of photography.
It was believed to have been dated 1839, but now an American scholar, Larry Schaaf, a Fox Talbot authority, thinks it may have been made more than 30 years earlier, possibly by Thomas Wedgwood, a member of the Wedgwood china family.
Wedgwood began experiment with making solar pictures in the 1790s, in the same way that Fox Talbot did in the 1830s, using paper made light sensitive by treatment with silver nitrate.
If Mr Schaaf is correct, the image of the leaf could date from the last years of the 18th century.
An image by the Frenchman Joseph Niepce, created on chemically treated pewter in 1826, is the world's oldest permanent photograph.
The image of the leaf was bought in London in 1984 for about £6,000, by a New York dealer. It would today be worth between £50,000 and £70,000. But if it is confirmed as the world's oldest photograph, “the sky could be the limit” in terms of price, according to Sotheby's photography expert Denise Bethel.
She said: “The possibility of a definitive conclusion regarding this early photogenic drawing is very exciting.”
The image was due to be offered for sale last month at a Sotheby's auction in New York. But it has been withdrawn pending further investigation.
Mr Schaaf, who was asked by Sothebys to inspect the leaf, said he believed a 'W' on the image may stand for Thomas Wedgwood.
Wedgwood experimented with photography while living in Bristol, but none of his work was thought to have survived.
Early photographs, such as the leaf, were produced on paper treated with silver nitrate to make them light-sensitive and left in the sun before being developed in a dark room.
As the exposed areas of paper darkened, a pale silhouette was left of the object. Semi-opaque objects like leaves produced great detail, as every tiny vein can be seen.
But continued exposure to sunlight darkened the images and early experimenters such as Wedgwood did not know how to fix them.
Fox Talbot is regarded as the father of modern photography because he conceived the process in which the original image could be duplicated many times.
His first camera photograph, a view of the oriel window at Lacock Abbey, Wilts, was taken in August 1835.
Until its sale in 1984, the leaf had been in an album which belonged to Henry Bright (1784-1869) a Bristol MP and a member of a prominent family interested in science and the arts.
Five other photogenic drawings from the album were sold in 1984, four of which also bear a 'W'.
Two are now privately-owned, one is in the J Paul Getty Museum and one in the Metropolitan Museum of Art in New York. Both museums will be doing further tests.
Dr Schaaf said the leaf did not fit into Fox Talbot's known body of work. The Bright family and Wedgwood shared mutual scientific friends.
