doesn't need to explicitly, it's enough to have the understanding that it's a "work for hire" situation (at least in the US)
of course just giving someone money is not sufficient to establish this, but telling someone that "I want to hire you to make a photo for me (of me)" and they acknowledge, then that is probably enough.
of course just giving someone money is not sufficient to establish this, but telling someone that "I want to hire you to make a photo for me (of me)" and they acknowledge, then that is probably enough.