Hans Thoma - Zwei Knaben an einer Bergquelle. It's very obviously a nude, but there is nothing to see. Previous brain imaging studies have pinpointed areas in the brain that specialize in detecting human bodies in the environment but it wasn't known whether the brain processes clothed and nude bodies in different ways. She looks almost angelic. See v2 by Hans Proppe in full res on Flickr.
Most of the images used in this post are used without explicit permission from the photographers, however, they are used under the 'criticism and review' sections of UK copyright legislation.
LSU Student Studies Completely Nude In Middleton Library [NSFW PHOTO]