Another way this is problematic: you begin with the claim,
God values humans out of His love for us and that we are created in His image. That value exists outside of human thoughts and desires. Therefore, it exists objectively.
And the more precise version of this, by your last statement, would be
God values humans out of His love for us and that we are created in His image. That value exists outside of human thoughts and desires. Therefore, it exists objectively to humans.
But then it would make just as much sense to say,
John values Mary out of his love for her. That value exists outside of Mary's thoughts and desires. Therefore, it exists objectively to Mary.
... and then repeat, for every human being who is valued by a different human being (which is true, I'd say, of every human being there is). It follows that even if God does not exist, every human being possesses objective value ("value which is objective to him or her").