If someone anonymously posted a naked photo on a website with my name and the picture is not me, what can I do to get it removed?

In order to legally get a picture removed from a website you would have to prove some legal justification for the action to be taken. From a legal point of view the posting would have to cause you some type of harm that you can prove in a court of law. You state that the picture is not you thus you would have to show that your name is such that it would be very improbable that someone else has the same name. Absent such a showing there is most likely nothing you can do about it.