best do the superimposing part in photoshop or some other image editor.

create a plane in max and load the photo in your viewport background.

(alt+b then load an image.)

use your perspective view navigation to roughly match the ground plane to the ground in your photo.

create a camera from the perspective view by hitting ctrl+c

place your football on the plane.

create a light souce with shadows turned on, try to match any shadow direction and colours in the photo.

apply a "shadow matte" material to the plane.

render the image and save it as a 32 bit pre multiplied .tga file

Load it in photoshop and use the alpha channel as a layer mask over your background image.

Using photoshop means you can use colour correction tools like colour curves or hue/saturation to match your 3d with the photograph for greater realism.

Hope that helps.

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