Positioning ofVideoGrabber webcam on different planes

Lets say I have a webcam that captures an image of something lets say a room like this -

Im having trouble then positioning that captured image onto different planes. for example, creating something like this -

Anytime I try to enact some code to make this - i cant get the image to be correct fitted onto the plane - its either wrong width or wrong height

Any help would be great

Thanks!