Ian Stirling wrote:


It's also possible (with a big camera admittedly) to do this from quite
some distance.
However, technology that would let a policeman carry a little thing that
would identify anyone within a couple of meters is quite possible.
Obvious countermeasures are dark glasses, and patterned contact lenses.
(It's hard to fake well, as the iris should respond to light and have a
pulse)

Yeah - according to John Daugman, inventor and holder of the core patent
which makes this work (and one of those rare cases where a patent is
used to general advantage, in that he seems quite fierce about getting
licensees to implement it right and f'r example includes a
"size-of-population-being-matched-against" parameter into the algorithm,
to keep the likelihood of a false match low as pop. size increases), the
largest distance it's practical for is about 20m, with pretty exotic
optics. As you say, a 2m "semi-covert" scan is possible; and anything
covert or semi-covert is easier to counter than a live scan with a real
person supervising it...