This photo was emailed to the staff here.
Several things are apparent from the image. First, it is highly compressed (38K) so there is digital artifacting from the JPG compression. Also, there seems to be no evidence of "collage" other than the inset photo of Diana and the text at the bottom.
Rescue workers appear consistent with those from France.
The top of the car was removed. Foam from it appears to be at the front left of the image. While other post accident photos show the top of the car present, you can see where cuts were made to remove it. We surmise that the top was replaced on the auto after rescue.
Placement of the air bags, bodies, etc. appear consistent with what we would expect.
It's probably an English scene, judging from the emergency workers and the "999" visible.
The angle of the shot is impossible in the topology of the tunnel.