Why don't you just use the plot function the way the help told you to? Why do you change it when you know that gives you incorrect display? plot() takes x as the first argument and y as the second argument so it's obvious that C(:,1) is the x coordinates and C(:,2) is the y coordinates. What happens if you just do it the way the example did it? Anything wrong with doing that?
In your case you should have 200 corners and each row in C is the (x,y) coordinate of one of the corners.
Did you try doing
out = zeros(size(I));
for row = 1 : size(I, 1)
out(C(row,1), C(row,2)) = 1;
end
