How to use ginput for image segmentation?

Dear all,

I tried ginput for image segmentation, but I obviously don´t know how to use it. My result is only figure with axes and curve. I attach printscreen of my result and the result of how it should look like. This is my code:

clc;close all;clear all;

figure
imshow('thorax-mdl.jpg')

[x,y] = ginput;

plot(x,y)

My result:

Required result:

Thank you for your answers.