Queen Victoria - unaware of their more furtive activities - praised the work of the pioneer Parisian photographers who invented new apparatus and chemical processes, published scientific papers and won prizes at international exhibitions such as the 1851 Great Exhibition at Crystal Palace.
The production of erotic photographs was confined to Paris. So Mr Nazarieff's revelations indicate that the British view of the French as a saucy, ooh-la-la lot has some basis. The spirit was not shared by the French judiciary: jail sentences awaited French pornographers. But the ultra-respectable founders of the new technology had a 'front': they registered photographs of chaste, academic 'artists' model' nudes at the National Library in Paris, thus securing not only copyright but freedom from prosecution - provided they sold the photographs only to bona fide artists and did not display them for sale.
The more libidinous, sometimes pornographic, poses that they had snapped during the same shoots were then offered 'under the cape' to well-heeled voyeurs prepared to pay up to today's equivalent of pounds 80 a print. Picture-framers were the most notorious distributors.
The most blatant clues linking demure 'artistic' prints to erotic prints by the same photographers are the studio props: the same patterned rug or curtain, fluted column or copper ewer appearing in both the artistic prints registered in the photographer's name in the National Library and in anonymous erotic prints.
Mr Nazarieff used these 140-year-old clues to build up tell-tale inventories of the studio props of seven eminent Paris photographers. His quest covered 3,000 images - daguerreotypes, pairs of hand-coloured stereoscopic (three-dimensional) prints, and large-scale exhibition prints.
Previously, few nude photographs of the mid-century circulating among collectors, even images filed in the National Library, had been identified as the work of named photographers. Most of those in the book are published for the first time.
Among the most cunning at covering his tracks was the distinguished Auguste Belloc (d. 1867). Like his contemporaries he had a respectable artistic background, having been a watercolourist. He gained his place in photographic history as pioneer of the wet-plate collodion process (successor to daguerreotype). He also invented a lustrous wax coating for prints, binocular stereoscopic viewing devices, a photolithographic process and a spring-back camera. He exhibited at Crystal Palace and published learned papers such as A Theoretical and Practical Treatise on Collodion-Process Photography.
Although Belloc was aware that 'artistic' nude photography had been legitimised by Durieu, whose images had been copied on to canvas by Delacroix, he took the precaution of using the false name 'Billon' when registering his stereoscopic nudes at the National Library. His deception might never have come to light had not Mr Nazarieff come across a consignment of 60 nudes known to have been sent by Belloc to a friend. They show certain props - such as pitchers and washbasins used in demure foot-washing scenes - that also crop up in kitchen scenes in which eroticism tends towards pornography. Impressed, the National Library has now changed its attribution from 'Billon' to 'Belloc'.
Louis Duboscq-Soleil (d. 1886) teamed up with the Englishman David Brewster when Brewster visited Paris in 1850 bearing the earliest stereoscopic prints, and made his own binocular stereoscopes. He developed a photometer and a refractometer. Exhibiting at the Great Exhibition of 1851, he demonstrated his stereoscope to Queen Victoria, who praised it. By 1856 he had sold 500,000 of them.
Samples of his work in the book include a hand-tinted stereoscopic daguerreotype shot at the time of Queen Victoria's accolade, showing a nude woman sprawled on her back on cushions as two black hands appear from behind a curtain. The giveaway exposing Belloc as the photographer is the patterned rug that appears both in this picture and in his shots of artistically reclining nudes in the National Library.
Belloc's sprawled-on-cushions pose, the book's cover picture, is strikingly similar to poses in today's top-shelf magazines. But a comparison of old and new genres would reveal that males in the age of the bustle had a greater predilection for buttocks than today's voyeurs.
Most open of the black-sheep photographers was Felix Moulin, who cavalierly refused to register his work at the National Library and, around 1850, published a collection of licentious daguerreotypes of non- professional female models aged 14-16. Some, shown in the book, found their way into the collection of Emperor Franz Josef of Austria. Mr Nazarieff describes Moulin as 'the first in the history of photography whose work exudes seductiveness'.
Police seized his photographs, which (during a trial held, ironically, in camera) were described as 'so obscene that even to pronounce the titles . . . would be to commit an indecency'. He was sentenced to a month in prison and a Fr100 fine.
When Moulin eventually condescended to register a series of nudes at the National Library, the photographic trade journal Le Propagateur of December 1853 published an exalted review. Of one photograph, which it called 'The Prayer', it said: 'Naked as Eve in the garden of Eden, chaste as innocence itself, a young woman in half-kneeling position lifts at once her head and arms to the heavens . . . Moulin does indeed understand the mission of art.'
Le Propagateur's only regret was that Moulin had chosen to entitle the picture 'Back Study' (Etude de dos). Fulsome trade- press reviews such as this sustained the respectability of Parisian nude photography. According to Mr Nazarieff: 'These were the X-rated films of the time.' I asked whether the more lewd productions of the big names would have been frowned upon by the influential French Society of Photography. Unlikely, he said. After all, the same photographers founded it.
Mr Nazarieff's research helped to put names to some of the prints owned by the German collector Uwe Scheid which were sold at Christie's last month. A mild, artistic Moulin stereoscopic daguerreotype of two pubescent girls with a classical vase fetched pounds 4,025. Half of an anonymous stereo card, an albumen close-up of a woman posing with legs akimbo and skirts aloft, made pounds 299.
Mr Nazarieff's book contains images dating up to 1861. But he particularly recommends study of the years between 1865 and 1870, at the end of the Second Empire of Napoleon III. 'There was some terrific pornography then,' he said.
Early Erotic Photography by Serge Nazarieff, to be published by Benedikt Taschen in December at pounds 9.99.