Diffraction limits are most visible for small apertures (high f-numbers). For surveillance cameras, I would expect* sensor size to be the bigger issue, because as long as sensor size is fixed, signal to noise will be limited by photon noise (the noise created by the randomness of photons themselves), no matter how good the sensor is.

Realistically, if this is a goal, then manufacturers will just increase the sensor size until the goal is met. This isn't a cell phone, so the sensor size constraints are pretty forgiving for this platform.

* Note: I am no optics expect, this is just what I've picked up on my own.

Here is a lens free camera http://www.technologyreview.com/news/525731/lens-free-camera...

It's incredibly tiny. As I understand it they etch individual pixels onto it, each of which can only receive light from a specific angle. As you make it larger and larger you can absorb more and more light at higher and higher resolutions, without dealing with lenses.

Although even lenses can do insane things like magnify individual cells to be human visible, or take pictures of distant galaxies. I don't know why everyone is so skeptical of merely photographing someone's eye.

Holographs are made right down to the spatial resolution of light, the interference patterns between light-as-a-wave from two different angles are what's laid down. So you could do a lot better spatially than what we do today.

Typical cell spacing is between 3 and 10 micro meter right now iirc and red light is around 650 nm, so about a factor of 5 to 10 or thereabouts.

Biggest enemies are not incident light quantity but thermal noise, as you get smaller in cell size that becomes a real problem (you can alleviate that with cooling).

> It seems there would be a point at which you reach maximum information density with camera sensors. Not due to limitations of technology, but the nature of light itself and the optics.

That is true--with a single camera.

At some point, we will have so many cameras facing an objective that you can exceed the limits of individual optics.

You can also try and integrate over time. Complex? Definitely. Not an exact science because you will have to estimate the motion of both the eyeball and the subject you are trying to identify? Yes (in most cases). Feasible? In some cases: probably.

And that, too, will get better with better hardware. At first, you may only be able to detect hair color and rough hair length in cases where the person being identified has a nice silhouette against an evenly lit sky, but that already is something.