Add a nice prior from a photograph, combine multiple measurements and presto you can pick out a person from a crowd with reasonable accuracy. No?
It applies to the sensor size as well. Such as you need a 3m sensor to get 100px per radian, under ideal circumstances, unless I'm mistaken. (I think I'm not)
There are techniques that can reduce that limit when you have multiple signals, though whether they can be combined with this technique isn’t clear.