"native resolution" of photos from digital cameras ?

This is, strictly speaking, not correct. Like many terms (SI unit prefixes...), resolution is used largely incorrectly in the domain of computing and without understanding of what it really means. It's a term which has been taken and used out of context. Resolution is a physical measure of the smallest object an imaging system can *resolve*. If two small objects next to each other are not distinguishable as separate objects (they are one blob), then the system has not *resolved* them. In the case of microscopy and cameras, the resolution (resolving power) is defined by the optics of the system (lens numerical aperture, plus any further diffraction and aberation). This is *independent* of the detector (CCD/PMT/film), but the detector will have to sample at least at twice the bandwidth to satisfy Nyquist-Shannon sampling criterea, so for a correctly set up system your detector will be sampling at twice the optical resolution in x and y. [For cheap cameras with massive CCD sizes, the optics are so poor you end up sampling pointlessly at many times the Nyquist limit; turn on 2x2 or higher binning to get smaller, less noisy and higher quality images. Compare with an SLR with better optics and a smaller [pixel] size but higher quality CCD!]

http://en.wikipedia.org/wiki/Angular_resolution
http://www.svi.nl/NyquistRate

Resolution is not, and never has been, a *size* measure as used by CCDs and monitors. I know it's common practice in computing, but it's wrong nonetheless. You can measure the well/dot pitch (i.e. distance between pixels), which would be better, but strictly speaking that's not really a measure of resolution either (in this context) since it's a property of an optical system and not of the detector/emitter of a light signal such as a CCD or monitor.

Regards,
Roger