a couple of observations: 1. stereo image is not a requirement for seeing and object in "3D". many people who don't have both eyes working properly (e.g. "lazy eye") still see the world perfectly 3D. there's much more to that than just a simple parallax.
2. dimensionality is not a property of an image. is a property of an object that the image represents. neither stereo pair, nor holography nor a simple snapshot is a true 3D representation (holography is the closest of the three). i believe, "3D" can be applied to any of them equally, as long as it is understood what is being ment. best, mishka
