How were the Ten Commandments given? Five on one tablet and five on a second tablet. This means that “Do not murder” corresponds to “I am G‑d your G‑d.” The Torah is telling us that one who sheds blood it is as if he has reduced the image of the King.
What is this analogous to? To a king of flesh and blood who entered a country and put up portraits of himself, and made statues of himself, and minted coins with his image. After a while, the people of the country overturned his portraits, broke his statues and invalidated his coins, thereby reducing the image of the king. So, too, one who sheds blood reduces the image of the King, as it is written (Bereishis 9:6): “One who spills a man’s blood . . . for in the image of G‑d He made man.”