[3DS] Questions about FriendPicture

[DaniElectra]

I'm looking at the 3DS friends server and I was interested on the friend "pictures", as I don't recognize seeing any pictures on the Friends List. I'd like to ask some questions about it:

1. What are the pictures contents?
2. What is it used for? Are the pictures methods called by the 3DS?
3. I'm trying to update a picture, but I'm getting PythonCore::TypeError. How is the image encoded? Does it need to have a specific format or resolution?