Blue and Green screen separations are one of the more familiar techniques known to the public. The art is in assembling the pieces seamlessly.
 

—The first shot below is simple enough. all we had to do was match the lens focal length and height to the background and make the studio lighting look sunny.
 

—In the second shot, the woman had to interact with the table in the background. Fortunately, with a computer handy, we could take a couple of test shots to make sure that
    the blue screen rig she was leaning on was where we wanted the table to appear and her hands matched the contour of the table.
 

—In the third shot, the young singer had to appear sitting IN a field of wild flowers. To "sell" this final comp, required shooting separate foreground flowers (blue screen)
    and blend them in front of the girl's hands and legs.