Blood spots usually just mean there has been a small rupture of a tiny blood vessel during egg formation, and this can happen even in healthy hens. They can also be triggered by too little vitamin A in your hens' diet. Occasionally, you may see a meat spot, which happens when there is a rupture along the wall of the oviduct. Both types are harmless.
Factory farms usually candle their eggs and discard most of those with aesthetic defects like blood spots, although with brown shelled eggs, it is harder to catch every defect. However, the spots are harmless. You can remove them if they disturb your sensibilities.