Combining 3D object with real photograph

Hi.. Its almost 5 month since my last post, showing how lazy I am to update this blog. I'm now focusing on 2D animation, but I never abandon 3D. Most of the time I use 3D to create object that is hard to draw, and then I render it using ink n paint.
But now I try to test something new to me. I'm trying to combine 3D object with real photograph. Its a tough job, and for this project I use my last 3D model, the old proton saga. Once I learn the trick, I try to apply on other render as well, and hopefully post it here.

Below is my test, I took a picture infront of my house, as the Background plate.
Then I render the model using mental ray matte/shadow/reflection shader.