I regularly see these (although, not usually as big), and they are considered safe to cook and eat as usual.
The American Egg Board (which is, just to be clear, a US government-backed lobby and marketing group, not a scientific body), states that
- blood spots are caused by ruptured blood vessels (which can happen for different reasons) of the hen (mother) at the time of ovulation (before the hard outer shell of the egg has formed)
- they are not an indicator of fertilised eggs
- they are safe to eat.
We don't see them (or don't see very large ones) regularly because they are normally detected by candling, and such eggs are removed (this is why blood spots are more common in eggs from local farms that might not be using such mass-production techniques).
Many other sites say things along the same lines, including the USDA. However, notice the other USDA comments on egg freshness and safety. Definitely make sure the eggs are cooked thoroughly (as always!), especially if they're from local farms and may have not gone through pasteurisation or other post-collection disinfection methods.
@BaffledCook might be right on the freshness comment (independent of the blood spot), although the photo you took is very bright and makes it a bit hard for me to tell how clear the egg white is or whether the yolk just broke when you cracked the egg.
The "err on the safe side" is usually a good rule to follow if you're concerned (it's just an egg!).