Most vision experts agree that newborn infants see the world upside-down for a short period of time. The exact amount of time that this occurs is unknown, although some speculate that it lasts only a few hours.
This phenomenon stems from the fact that the human retina does, in fact, capture an image that is upside-down from the one the eye sees. The process by which the image is turned right-side up in the brain is one the eye must learn, and it is thought that newborn infants take a short period of time to adapt to that fact.
Some people suffer from a condition called "Print Inverted Reading" or "PI Reading," which occurs when the person can only read if text is presented upside-down. It is thought that this is an inability of the eye to properly process the image.