The Israelites were required to be cleansed with the ashes of a pure red heifer if they came near or touched the dead body of an animal or human. We often hear about the pure red heifer concerning the temple's rebuilding; it's mentioned in Numbers 19. It is specific to the unbelieving Jews because Jesus was symbolic of our red heifer; "Christ, as man, was the Son of Adam, red earth, and we find him red in his apparel, red with his own blood, and red with the blood of his enemies." Matthew Henry. There was another good reason that God used the red heifer as a symbol of purification for sin; in Egypt, they would sacrifice a red bull to their god, but never a female. God had to make a distinction to show who was in charge and to change their mindset from the Egyptian gods to his ways.
One thing interesting about this particular sin is that you may not know you've sinned because walking over a grave could cause you to be unclean, and the only way to become clean was to wash with the ashes of the heifer that had been mixed with running water. How would you know? It makes so much sense why when Jesus came in contact with a dead person, he raised them to life; he did not even have unintentional sin. I guarantee you that every step Jesus took on earth was meticulously coordinated to avoid unintentional sin because he was our pure sacrifice. We were disgusting filth in the eyes of God before our salvation in Jesus; he purifies us from things we don't even know are sins. For this reason, we are under the New Testament covenant; the Old Testament law is not good enough to purify us from all sin; only Jesus has that distinction.
But the man that shall be unclean, and shall not purify himself, that soul shall be cut off from among the congregation, because he hath defiled the sanctuary of the LORD: the water of separation hath not been sprinkled upon him; he is unclean. Numbers 19:20
The calf in the picture would not be a pleasing sacrifice because of the white on his face; plus, it is a boy.