It's hardly a secret that photos are often heavily retouched before publication, but it's relatively rare that a source image is available, allowing direct comparison with the final version. Here's a particularly blatant example.

The image on the left is a studio photograph of Keira Knightley, taken for use in material promoting her recent film, 'King Arthur'. On the right the same photo is incorporated into a poster. I've slightly blurred the backgrounds, for clarity.
I don't know who holds copyright, but I found these images at a fan site after seeing lower-res copies elsewhere.
Incidentally, a UK 'newspaper' claimed these images show the UK promotional material vs. the US version. Not true.

Some have expressed doubt that they really are the same image, or that only the head is the same, superimposed onto a different body. However, the reason I can quote precise angles of rotation in the following paragraphs; indeed, the main way I noticed some of the smaller details, is that I superimposed the source and end images in Photoshop and reproduced the transformations myself. There's absolutely no doubt that one image is derived directly from the other.

A few changes are uncontroversial: the image has been rotated through 4.3° to improve the overall composition. The colour balance has been reddened to provide a warmer, subliminally more exciting tone and to draw together the disparate elements of the collage. The photo itself has been neatened slightly: a stray lock of hair has been removed, as has her sword. Unflattering details (e.g. a shadow in her armpit) have been diminished, whilst flattering ones (e.g. eyes and mouth) have been accentuated. Warpaint, worn in the film but not for the studio photo, has been added subtly.

However, the main changes go beyond 'accentuating'. Someone has decided that the slim actress doesn't quite meet the Hollywood ideal physique, so her breasts have been enlarged whilst her waist has been narrowed; not to the point of caricature, but when the source and end images are seen together, the manipulation is very obvious.
There's a second, deceptively simple trick. The whole photo has been rotated 4.3°, but the vertical line of her modified abdomen alters the apparent angle of her hips (by 8.3°, if anyone's counting). On the left, she's leaning into the bow, with slightly rounded shoulders. On the right she's upright, with shoulders seemingly further back, changing the emphasis of the original pose.

I'll let others decide on the aesthetics, ethics or even necessity of this manipulation.