You are driving the car from which the picture is taken and see the overtaking being performed. How should you act?
Review of the options:
Drive normally and ignore the overtaking. – Not good, since the situation may be dangerous. A potentially dangerous situation must never be ignored.
Drive in the middle of your lane and beep or flash your full beam headlights. – This is an aggressive option, which is never good in traffic. It also does not seem that the car that is overtaking is performing a dangerous manoeuvre since the car is not crossing over into your lane. “To avoid traffic accidents, a road user shall observe the care and caution required with respect to the circumstances.” (Swedish Road Traffic Ordinance) = you have to “give in” even if you are in the “right”.
Keep to the right of your lane and be prepared to act. – Good, this creates a good safety margin while preparing you for action if something should go wrong.
Reduce your speed and drive out on the hard shoulder. – This is an overreaction. As stated, the car that is overtaking is staying in the correct lane, while at the same time the road is wide enough for it to be enough that you keep to the right of your lane instead of driving out onto the hard shoulder. Reducing your speed may do more damage than good since the risk of being hit from behind increases.