TRANSMISSION POPPED OUT OF PARK WHILE BEING UNATTENDED AND ROLLED BACKWARDS AND STRUCK A PARKED VEHICLE. THE VEHICLE WAS IN PARK WHEN THE DRIVER EXITED THE VEHICLE WHILE WORKING TO PHOTOGRAPH ANOTHER VEHICLE FOR HIS JOB DUTIES. WHILE THE DRIVER WAS OUTSIDE OF THE VEHICLE TAKING PHOTOS, THE CAR POPPED OUT OF GEAR AND ROLLED BACKWARDS AND STRUCK A PARKED VEHICLE.