Felix Grant , Oct 26, 2008; 04:31 a.m.
While the brain, I agree, /is/ the best available processor it's that fact alone that makes human vision so good. The eye itself is /not/ the best available optical device by a very long way – it only appears so because the processor woks miracles of synthesis to clean up the information.
For example: the human eye resolves, at best, about 8 lines per millimetre – and over most of its field of vision much less than that, and it declines with time from about age 20 onwards. A 35mm film camera, by comparison, resolves around 80-100 lines per millimetre in average hand held circumstances. The rich and detailed vision we enjoy relies on the eye always being on the move, capturing partial and low grade images which the brain combines in order to produce an enhanced final view of the world.
I'm not just saying that for the sake of disagreeing –it's relevant to your main question.
What makes the difference in a "snap"? Precisely, in my opinion, that: it is a snap, a single moment fixed, which the eye alone cannot do. We see, in a real sense, in digitally synthesised video; photography cuts across that by presenting us with the impossibility (in nature) of high fidelity stillness.