How to extract point from a group of plot graph?

I have a folder with some .png files. Please check the attachment of the folder. How can i exrtact the coordinates of the line from the figure. I have tried with the following code:

   h = findobj(gca,'Type','line');
   x=get(h,'Xdata');
   y=get(h,'Ydata');

But with this code im getting all the coodinates from the plot. How can i extract only the coordinates of the line that is plotted in the figure i.e., the coordinates of the blue dots in the figure.

Answer 1

[KSSV]

I = imread('fig500.png') ;
I1 = rgb2gray(I) ;

[y,x] = find(I1==29) ;

imshow(I)
hold on
plot(x,y,'.m')

[SUSHMA MB]

It didn't work....Im not getting any coordinates with it.