Check out blood spots and meat spots on this link. That looks like a blood spot to me but the color is a bit different, may be the lighting.
Egg Quality Handbook
http://www.thepoultrysite.com/ourbooks/1/egg-quality-handbook/
When the membrane that is around the yolk separates to release it to start its journey through the hen’s internal egg making factory a tiny blood vessel occasionally breaks. This can get some blood in the egg. Occasionally a piece of something inside the hen’s body cavity gets sent down that egg making factory, that’s a meat spot.
These things happen quite often. The reason you don’t see them in the eggs you buy is that those eggs are electronically candled to remove any that have something in them. They don’t want those kinds of surprises in the commercial eggs. As far as your health goes there is nothing wrong with eating those eggs. The eggs that fail candling are sold at a reduced price to places that break the eggs before using them, such as bakeries. I agree there is a Yuk! Factor when you see one of those. That’s why I suggest you always break one of our eggs in a separate bowl before you use it.