Paintings vs. Photos

[Serena Moonsilver]

No: HPFGUIDX 76735

I've not seen this posted, but I'm sorry if it's been discussed:

Why is it that painted portraits can talk but photos can't.  And in 
that case, why doesn't everyone have a portrait painted of 
themselves to they can leave a bit of themselves behind after they 
die.  I mean maybe there are portraits of James, Lily, and Sirius 
out there that Harry could talk to.  Or at least some of his 
relatives.

Also, if you have a portrait painted when your say, ten, does it 
know everything you know until you die or is just everything you 
knew up to age 10.  Or maybe it's like Dorian Grey, only the picture 
just stops aging when you die.

Thoughts,opinions?

Serena