For myself, as a life-long celibate, I have a hard time believing that any sex is part of the image of Christ. But that is an emotional reaction; there is 1 Corinthians 7 providing an approved channel (marriage) for the sex drive and the indirect evidence throughout the Bible of men and women blessed of God, who were clearly sexually active within their marriages.
Plus there is the evidence of good Christians even today who are sexually active within their marriages, and I can see how strong the sex drive is throughout society. And nowhere in the Bible is marriage restricted in terms of who may contract (covenant) a marriage. [Even the so-called incest prohibitions are prohibitions against adultery within the family. Your uncle's wife, or your sister-in-law are not blood relations, and the levirate marriage laws show that when their husband, your near relative, dies, not only are you allowed to marry them, in some cases you are required to.]