Christopher Huet is considered to be a master at photo retouching. He’s used by all the top ad agencies in the world and there’s no doubt you’ve seen his work in ads for anything from Adidas to Guinness.
Huet says of his work,
My purpose is to make people forget the retouching itself even if it seems obvious because of the singularity of the image.
He certainly succeeds in combining elements to make seamless images. Be sure to look through his portfolio site because he shows the step by step process for retouching each photo. It’s really quite amazing to flip back and forth between each step to see the transformation.