Experts who examined one of his "six-footers" - the iconic 6ft landscapes which helped establish his name in the 19th century - found hidden images of two figures in the centre of the canvas that he later painted over in order to make the painting more dramatic and eye-catching.
The original sketches for View on the Stour near Dedham are very different to the finished version by the painter, who was wracked with neurosis and stress for most of his working life, in which he competed for attention with the likes of Turner.
Tate Britain, which revealed plans yesterday for a new exhibition featuring his "six-footers", used X-ray equipment to uncover the secrets of nine masterpieces, including The Hay Wain and The White Horse.
The exhibition follows a series of shows in which the works of major artists, such as Blake, Turner and Gainsborough, have been reassessed by the Tate.
The full-scale sketches and completed paintings have been brought together for the first time since leaving Constable's London studio in the early 1800s.
They are among the highlights of the exhibition, Constable: the Great Landscapes, opening on 1 June, which has borrowed works from 13 art institutions in Europe and America.
In View on the Stour near Dedham, Constable initially drew two boys fishing by the water's edge and a girl close to a wooden beam in the foreground. In a subsequent sketch, he replaced them with two young boys sitting on the edge of the river bank.
In the finished work, the boys have disappeared, with Constable adding a barge in the centre.
Anne Lyles, co-curator of the exhibition, said the changes represented a significant turning point in the evolution of "big picture" canvasses. "By eliminating figurative detail in the foreground, Constable wanted to simplify the composition to make it more dramatic," she said.
Sarah Cove, the founder of the Constable Research project, said that the painter was "completely stressed and neurotic" and wrote hundreds of letters to friends, reflecting his anxiety and "manic nature".Reuse content