The same tool that I used to make this duck skinnier (liquify) is used in modern ads of beauty and magazines. I think using photoshop to make something prettier is fine as long as it isn't what you are advertising specifically or it isn't said to be real. Let's say you are advertising clothes but you photoshop the face of the model that in my opinion is fine and maybe even good, but if you are advertising face makeup or plastic surgery then I believe that it isn't okay. I think they should also credit photoshop. Overall if anything photoshopped and released to make more beautiful follows these guild lines then I think it is okay.
My favorite element of art is line because it is so simple and clean. My favorite principle is emphasis because it is also a simple concept that you can make really unique and cool. Elements and Principles Link.