I was recently diagnosed with and treated for a malignant tumour in my left eye. Nothing was visible from the outside except with opthalmic instruments. It was visible from the inside though. One thing that could cause the appearance of a white spot in your pupil would be a cataract ie. a cloudiness of the lens, but you would notice a haziness in the vision from that eye long before it was noticeable from the outside. I have a cataract as a result of the treatment for my tumour which is barely visible to the naked eye yet has rendered the affected eye virtually blind.
Has this white spot been visible in other photos? if not it could simply be a reflection of a bright light off the cornea.