The Pinkie 'Smile' Wallpaper is something I have created using images from *semehammer, so if you want permission to use it, I would recommend asking her instead. I personally do not mind if you use it, so with her approval, yes, you can certainly use it.
*randomly going through messages from groups* "Oh hmm, a humanized Pinkie wall paper? I should get a closer look" *Click* My god...it's everything... It's too awesome! Can't handle!!!! GAAAAAAAAAAAAAAA