I don't get visual flashes, though the energy of the person often indicates their personality. I see..colours and sense emotions in people. Troubled people for instance have like a thundercloud type of grey around them. Manipulating people have often this icky red-brown feeling. People in pain make me feel pain as well. Things like that. Aside from that, certain types of behavior give me insight into the trauma they've been through in the past. I guess the flashes happen here, for me. That combined with the color thing can occasionally give me an insight into who they are a person and what made them so
There is also an intensity and freshness to colors that are a temporary or new state of being surrounding the person and a stained, matte, almost worn out feeling to those that are permanent. Kind of like clothes that have been worn past their prime. As for behaviors, they act like bread crumbs for my radar. I have a kind of..radar type thingy, blinking in the areas where peoples personal pain is hidden. I often don't know what it is, but I can gauge the size and depth of the wound.
Edit: As for how close one has to be: the more time you have to actually observe them and probe them, the more detailed the picture becomes, but it is possible to do this with even strangers in the street.
I also find that the more time one on one I get, the more accurate I get, and physical proximity helps. In fact, I get most accurate (and most overwhelmed by their emotional state) when physically touching.