The full frontal image was taken by Lee Friedlander and appeared in Playboy in 1985.
Matthieu Humery, head of Christie's photography department, says Madonna was a 20-year-old dancer trying to make ends meet when she answered Friedlander's newspaper ad seeking a nude model in 1979.
He says six photos from the shoot were sold to Playboy and the one up for auction Feb. 12 is "maybe the most explicit one."
Another photo of Madonna, by Helmut Newtown, is also in the auction. In that shot, she is wearing lingerie.
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