Photos vs. Portraits

[larriepam2000]

I got thinking last night about portraits that can talk, move, learn, 
travel, etc.  Why can't photos talk?  People can be told to move 
around by a wizard/witch (OotP) in a photo, so why can't they speak?  
Did Lilly and James have a portrait so they could talk to Harry if 
anything ever was to happen to them? And if not, why not? James and 
Lilly must have enough money to have one done. They made arrangement 
with Sirius for him to be Harry's Godfather so why not one step 
further?
I am sorry if this has been talked to death but (what hasn't) I 
couldn't find anything in the archives.