How ‘alive’ are paintings?

[ravenclawblack]

No: HPFGUIDX 69718

Hello everyone,

I am curious as to everyone's thoughts on the paintings in the
potterverse.  Until book five, I thought of the paintings a bit like
automatons.  The fat lady was like a computer program that checked who
could be let in the door, and the other paintings didn't do much.
 But
now, in book five, the paintings seem very lifelike.  Phineas
particularly comes to mind.  Are the paintings like ghosts?  Can
wizards choose to leave themselves behind in that form, or are they
copies of the wizard's personality?  Can a painting be done while
the
person is alive, or postmortem?  (I'm thinking about Sirius here)

Anyway, I would like to hear what others think on this topic.

-Colin