Hi,
If my understanding of your question is not wrong.
Irgb = imread('rhsr9t.jpg');
Icrop = imcrop(Irgb,[75 25 670 500]);
Igray = rgb2gray(Icrop);
Ibw = im2bw(Igray,graythresh(Igray));
Iarea = bwareaopen(Ibw,300);
Idilate = imdilate(Iarea,strel('line',10,0));
stat = regionprops(Idilate,'Centroid');
linecoor = [0 stat.Centroid(2);
stat.Centroid(1) stat.Centroid(2);
size(Irgb,2) stat.Centroid(2)];
imshow(Icrop); hold on
plot(stat.Centroid(1),stat.Centroid(2),'ro','markersize',10,'linewidth',2);
line(linecoor(:,1),linecoor(:,2),'linewidth',2,'color','g');
And the result :
