How can i find the intersection point between two lines ?

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I have some horizontal images and i draw a vertical line upon them. But There are some angle exists among the horizontal lines and vertical line depends on that horizontal lines. So I applied some intersection algorithm , collected from internet, but the output of intersection not good for all cases of horizontal lines. Since I consider three angles as like uploaded images.Here you see that, some intersection points are up and down. I want to fix it at proper place. I mean i want to develop a intersection code which will give proper output for three cases. I have already tried this given code,It will be great for me if someone explain the code how it works basically, because i just collected it from internet.

x1  = [v(1,1) v(1,2)]; %vertical line X intersection point.
y1  = [v(2,1) v(2,2)];%vertical line Y intersection point.
%line2
x2 = [h(1,1) h(1,2)];%Horizontal line X intersection point.
y2 = [h(2,1) h(2,2)];%Horizontal line Y intersection point.
%fit linear polynomial
p1 = polyfit(x1,y1,1);
p2 = polyfit(x2,y2,1);
%calculate intersection
x_intersect = fzero(@(x) polyval(p1-p2,x),3);
y_intersect = polyval(p1,x_intersect);
P(1)=x_intersect;
P(2)=y_intersect;