Yea i agree thats a really good idea. I just don't really buy it though. It makes sense but their's a lot of different types of pictures in the Wizarding world. I mean, I remember in PoA, their were pictures of Sirius on the front cover of the Daily Prophet and they could move and stuff. But i doubt if Harry were to find one of those he could talk the the soul of Sirius so I don't think its for all paintings/photographs that the soul is imprinted on. But, going on the facts that these people can only be in one of their portraits at once, it makes sence that the portraits would have to have some sort of soul. It would seem like the people in photographs don't have souls, but then Percy can leave his portrait and that obviously show's theirs more than just a mindless body in the picture. My best guess is it's just an imprint of a soul, sort of a copy. I have absolutely no idea though, this whole thing is really confusing and my post is seeming to confuse me more as it seems that every theory i have has something that contradicts it. I'll have to think more on this lol.