This seems to be an interesting, unexpected challenge. There seems to be a lot of legal nonsense when it comes to a simple little picture on a simple little story. If you don't own the picture, you need rights. if you need rights, you need to ask for them. to ask for them you need to track down the owner and probably pay them for rights. if you manage to do those steps, you still have to alter the pic for your needs, either DIY or pay someone to do it.
perhaps ill just make a happy face in windows paint and call it a night.