When I think of a person, I think of their odd smiles--some that reach their eyes and others that don't. I think of the small movements that couldn't be captured on a still photo, but that would lose meaning in repetition--the jerk of their eyes when they are catch looking, the flail of their arms when excited, and just the way they hold themselves--loose and curved or tight and angled. I can never have a real sense of a person until I've seen them move.
Whenever I draw a character or a person--or write them--if able, I'll find clips of their scenes. I try to get a sense for how they move, for the motions that accompany their words, their thoughts. I try to find the language of their body so I can mimic more then just the way they look or the way they talk.
Then, there's all the other senses...
The unique scent a person has--chosen scents, like perfume, mixed with deodorants, sweats, and even their own unique scent--and sometimes their scent is even added to by the things they surround themselves with: books from the library, carpet from work, ink from printers, grass from sports, plastic from toys and games, smoke from soddering bits of metal together.
There's also the sounds from them, and not just their voice, but the soft sound as their lips open to spew words, or the clop, clop of their shoes rounding the corner, or the jingle of their bracelets or rings as they gesture to things.
Then of course, the feel of them--and not just the physical means, but the warmth they bring into the room, or the way they can open a conversation up just with a lewd comment or eyebrow wiggle. And also, the calluses on their hands, the fondness in their ruffling of hair or the grudging friendship in the prod of their toes in your back.
I simply can't understand a person until I've known all of these things. And that's not to say you can't understand people online--but its a different understanding, a baring of minds that leaves nothing to the imagination.
These ideas extend to any living being, be them human, feline, lapin, or plant.
Perhaps this is why I utterly fail at photography.