Ps 139 and the image of God

It's common for Christian ethicists and theologians to ground human rights and dignity in the image of God. And it's true that the image of God is something that sets man apart from other creatures. There are, however, problems with making that category the locus of human rights and dignity. For one thing, Genesis never defines the image of God, and it's not entirely clear what that refers to. Minimally it seems to mean that man is God's representative on earth. But that's a rather thin basis for human rights. 

One reason the image of God is made the go-to locus of human rights and dignity is that most ethicists and theologians don't try to define it exegetically. Instead, they begin with philosophical anthropology, and define the imago Dei by reference to distinguishing traits identified by philosophical anthropology, like reason and freewill.

Another problem with centering human rights and dignity on the imago Dei is that it leads to the neglected of better, richer prooftexts. The locus classicus for human dignity ought to be Ps 139, not the image of God. This is not to say the image of God doesn't figure in an overall account of human dignity, but overemphasis on that category, which is typically defined in terms extraneous to Scripture, sidelines Ps 139. But that's a much firmer basis for grounding human rights and dignity, instead of the rather elusive and slender category of the imago Dei.