How close is the estimated distance (to the actual distance) when you're eyeballing it like that?
How do you know how much of the lighthouse is below visibility? I presume all lighthouses are not the same height......and...do you count the black and white stripes down as some kind of standardized measurement per stripe?
here check this and you will see how indeed that photo you published is a flat earthers worst nightmare as this is an age old method of measuring distance from a boat to the coast !!
http://www.skysailtraining.co.uk/dipping_distance.htm