Plot an Ellipse to show orientation of an Image

Hi, I am trying to plot an ellipse to show the orientation of an image.

I have tried this code

im = iread('Dog.jpg','grey','double') %Reads the image and converts it to greyscale
ithresh(im); %used to determine the threshold value to represent the dog
im = (im<0.5); %Performs the segmentation
im1 = (im<0.5);
idisp(im) %Displays the image

%Plots an ellipse that shows the orientation of the dog
f = iblobs(im);
hold on
f.plot_ellipse()

But the ellipse won't show.