This is more or less how magazines are manipulating their images so that the models look "perfect" in their eyes and other areas. A nice example of this in Adobe Photoshop is available at . I strongly recommend using the latest version of The GIMP.
Load an image that you want to manipulate. Go in <Image> Filters > Distorts > IWarp (for Adobe Photoshop and Photoshop Elements users, this is the equivalent of the "Liquify" filter).
You manipulate the image in the preview. In the "Deform Mode" section, choose "Move", this will deform the image in the direction of the movement of the mouse. For the purpose of body shifting, "Remove", "Grow" and "Shrink" are the other interesting buttons. They do what it says on the tin. Adjust "Deform radius" and "Deform amount" to your likings, depending how subtle your edits have to be. Also the "Swirl" options produce interesting results. If you want to start over (e.g. you messed your image up) click on "Reset".