Mais um link excelente, obrigado Lacyowl!
That's interesting. If I've understood what you've said in other discussions, "Eu tiro a sua foto" (I take your photo) can't be translated as "Eu tiro a foto de você" because "de você" is not a possessive. But "de você" can replace "sua" in "Eu tiro uma foto sua" because it is treated literally as "of you". Is that right?