Is there an app for iPhone or iPad for this?

I'm on vacation and I don't have my laptop with me. I really want to take a picture and put it into Lock Screen Designer and use as a wallpaper. I generally use Gimp at home, and I dint know what the feature is called, but it's where you can cut out (not crop) a part of a picture, in this case a person...? It doesn't matter if it's for iPhone or iPad, and I've already tried PS for iPhone. Any other ideas? Thanks guys!