UPDATE: This photo was not actually in the Lost Promo/Trailer sorry.
This was one of the hidden images. 
Thanks to a number of people we've found out what the painting is. Taken from Wikipedia.Venus at her Toilet, also known as The Rokeby Venus, is a painting by Diego Velázquez in the National Gallery, London. It dates from 1648 to 1651.
In the painting the goddess Venus is depicted lying on a bed, looking into a mirror held up by Cupid. The face reflected in the dimmed mirror appears to be that of an older woman, which has long intrigued experts. Some think it is a commentary on the vanity of beauty which is transitory due to aging. Some think the face in the mirror was over-painted by another artist at a later time. Another explanation is that the face is not aged, merely out focus, a sharper face would distract our immediate attention from the form of Venus, by seeing the nude first, and the face afterwards we are "caught" in voyeurism. The face in the mirror is also substantially larger than it should be, and the mirror is angled such that, in reality, it would reflect a different part of the goddess's body.
Source: Wikipedia
