Nude (with long hair functioning as breast drapes).
Swimming and movie star Annette Kellerman, embracing the naturalist movement, goes for a nude dip in the movie A Daughter of the Gods. Waterfalls (1), and poses sitting on a tree (2, 3).
Kellerman's apparent hip-length hair performs a roll in covering her nipples and pubis, but not always as you can see. And "not always" is what made people rich and famous.
Other stills from the film include a conversation with Mark Price and Stuart Holmes (4) and an embrace (5)
In vector momentum terms Kellerman begins in the movies fully clad in 1909, bares her legs in 1914 (AK1410) and is fully nude in 1916. Covered to not-covered in seven years--and that's not just the story of Kellerman, it is the story of the era.
Kellerman's nudity is not Hollywood's first (MU15-21), but she is the first big-name star to appear à natural on the big screen--nor the last (e.g., CB2755). And the first to display an active role as opposed to a static poser, a relative modesty difference. A Daughter of the Gods is the highest budget picture ever made and it, and a handful of others are road-show attractions with a $2.00 ticket (1916 dollars).
Documentation of Kellerman wearing soutien gorge and skirt costumes also emerges about now (AK1620).
Herbert Brenon, writer and director, A Daughter of the Gods, Fox Film Corporation, 1916, [Lo Doca probably incorrectly site date as 1914; given that the "first nude" credit is at stake there is temptation to wiggle the date forward and claim the prize.] .10 from Lo Duca and Maurice Bessy, L'erotisme au Cinema, Filmarchives, Paris, 1977, p. II-48. .20 from Arthur Knight and Hollis Alpert, "The History of Sex in Cinema, Part Two: Compounding the Sin," Playboy, May 1965; it is also reproduced in John Kobel, Hollywood: The Years of Innocence, Abbeville Press, NY, 1985, and attributed to photographer Witzel. .30-.50 from Daniel Blum, A Pictorial History of the Silent Screen, G. P. Putnam's Sons, New York, 1953, p. 98. Scans of .10 and .20 also at fortunecity.com. 5 pictures.