PicMonkey has lots of options!
".... we've tried our hardest to put you and your images in the realm of the unreal. We're talking about how to illustrate your photo in the style of a stencil, poster, graphic novel, or Warhol print. This short tutorial packs six effects into three minutes, so get ready, get set, and get illustrated."
Along with Lunapic, PicMonkey gives you great options for creating illustrations to insert in your BookCreator masterpiece. (You'll have to do the editing on a laptop or desktop and then import/email to your iPad.)