I'm leaning toward recession, but most people on here like to jump the gun and label almost all hair loss as male pattern baldness and then they recommend finasteride. It could be maturing hairline, as you are blonde and hair density tends to look worse with blondes anyway at corners, and it isn't *that* far back. But your frontal forelock is also thinning (see the small hairs?) which is really strange. That means it's either really aggressive hair loss or you are maturing at a really fast rate and it could stop. I would see a derm or seek more opinions. Good luck!