How to put a picture IN another one?

Like to make it look like i'm holding the sun, or i'm in another persons hand. If there's an iphone app, can you please tell me?

There's no app that I know of, but you can easily do that using a computer program like photoshop or if you're young like me and want a free program, use gimp. I use gimp for everything. Just look up tutorials and you'll figure out how.