Casting shadow onto background
I'm experimenting with building a character and using a background image. I want my character to cast a shadow onto the background image as if she's standing in the field shown in the image.
The "problem" is that the "plane" is visible in the final render. Without the plane I can't create a shadow, and with it, well, the results make it look like my character is standing in a dull gray square.
What's the correct way to have my character case a shadow on the background image?