While the report did look into the possibility of some type of debris on the film or its film plane back-plate was discussed and disregarded, they never looked at the camera itself.
The camera system has a very unique optic system that looks very similar to the object in the photograph.
Because there were no eyewitness reports from the ground or the members of the mapping team there is not much of a chance of this being an object of approximately 683 feet in size or even something that was an actual object of any size flying in the air beneath the plane.
The problem that report had with the object not creating a shadow is easily explainable if the image was created by the optics of the camera and not a physical object below the plane.
The object in the image appears to have been created by reflections of ambient light inside the optics of the camera system caused by a unique combination of the type of camera system, angle of the plane to the light, position of the sun and possibly the angle of the light coming from the surface of the water located beneath the plane.
Source : http://www.rockymountainparanormal.com/1971costaricaufo/index.html