1. A method for performing oximetry on blood of a blood vessel within stationary tissue of a subject, comprising the steps of: (i) at separate times, acquiring images at a first wavelength of said blood vessel within said stationary tissue; (ii) at separate times, acquiring images at a second wavelength of said blood vessel within said stationary tissue; (iii) automatically, eliminating spectral information relating to the stationary tissue by generating respective differential images of said blood vessel within said stationary tissue at said first and second wavelengths, based upon said images acquired at said first and second wavelengths, said images resolving discrete particles within said blood vessel, said particles selected from the group consisting of erythrocytes and aggregates of erythrocytes, even when said blood vessel does not show significant pulsation; and (iv) performing oximetry with respect to said discrete particles by: (a) performing spectral analysis on each pixel of said differential images, the spectral information relating to the stationary tissue having been eliminated; (b) calculating, from said spectral analysis of said differential images, quantitative relative levels of two blood-related chromophores in said particles of said blood vessel; and (c) generating an output in response to the quantitative relative levels of the two blood-related chromophores in said particles.