example...this was done using an an enlarger and a bit of practice.

This obviously fake composite with wrong lighting, mismatching grain, terrible contrast which just looks fake is a perfect example of how difficult it is to combine two images.
To get Oswald to fit into the scene seamlessly requires photographing Oswald in the exact same position with what would have to be perfect recreated lighting and as seen in Jerry's example above, it ain't as easy as your imagination wants it to be.

JohnM