It's been claimed on politics SE that the body of the dead becomes the property of his family. No country was specified, but is there really a country where this happens?
In the US, Pennsylvania specifically, the court in Pettigrew v. Pettigrew, 207 Pa. 313 says that
the law recognizes property in a corpse, but property subject to a trust and limited in its rights to such exercise as shall be in conformity with the duty out of which the rights arise.
Larson v. Chase, 47 Minn. 307 likewise states
in this country it is, so far as we know, universally held that those who are entitled to the possession and custody of it for purposes of decent burial have certain legal rights to and in it, which the law recognizes and will protect. Indeed, the mere fact that a person has exclusive rights over a body for the purposes of burial leads necessarily to the conclusion that it is his property in the broadest and most general sense of that term, viz., something over which the law accords him exclusive control.
This is in contrast to the English legal tradition where the church has jurisdiction over a corpse, giving rise to a doctrine that a corpse is not property, citing a dictum from Lord Coke that
It is to be observed that in every sepulchre that hath a monument two things are to be considered, viz., the monument, and the sepulture or burial of the dead. The burial of the cadaver that is caro data vermibus is nullius in bonis, and belongs to ecclesiastical cognizance; but as to the monument action is given (as hath been said) at the common law, for defacing thereof.
This article provides further analysis and case citations, mostly in the US. The topic of body-ownership is the subject of a book-length analysis (ten Have & Welie, Ownership of the human body). I think, according to this article, that under Islamic law, a body (living or dead) is not property, so an advance directive is not an absolute right.