This is a shot I worked on last year. I only worked on the blue Focus. Basically the image originally included a photographed pre facelift version of the focus and they want the 08' facelift model there instead. However because nearly every panel is different on the new focus I basically replaced the entire old car with the new cg one. The windows are from the original photo, everything else is CG.

Worked on in 3d max and rendered in mental ray.