Emma Watson goes topless

Emma Watson has stripped off for charity.

The 22-year-old star - best known for her role as Hermione Granger in the Harry Potter franchise - has been photographed topless and covered in muddy water for a series of portraits in a new photo book and exhibition called Natural Beauty.

The photo is part of a series of celebrity photos for the book, with all proceeds donated to Global Green USA.

The actress is clearly excited to be involved with the campaign, as she tweeted a photo of herself from the shoot, with the caption:

"'My friend is supporting GlobalGreenUSA with his book Natural Beauty. It's out now. : ) X' (sic)"

Click on the thumbnail below for a larger version of one of the gorgeous images: