Cg shadows with photo

I have recently finished working on a TARDIS model and I wanted to put it into a photo.

Well I have a problem with shadows.
I would take a plane and use that to recieve the shadows but with raytracing on it not only shows where the shadow is but the whole plane will darken the image.

I can do it just fine using the shadowbuf on the spot light instead of ray shadow, but I want to use AO. And no matter what I do I can’t stop the plane from darkening the image while raytracing is enabled.

What should I do?

render a black and white AO/shadow only path by setting all the model to white, which will give you something like this:

then combine this with your photo using a ‘multiply’ blending mode.

render your cg objects without the background and compose it with the previous image

this is what you get with a little color correction.

Well I would like to do some animation with my model but I still need raytracing for a light setup I have with my model.

What I would like to know is why the plane darkens the image for instead of just the shadow area.

Edit:I fixed it. It was the fault of a lamp in my scene.