detecting the corners

I have door image in different environments ,i want to detect the corners,and draw a bounding box,i used corner(I),rectangle command,but not getting exact result ,please help

my images

http://imgur.com/JLDQf

http://imgur.com/QSx95

please help

Answer 1

[UJJWAL]

MATLAB supports two standard methods for corner detection. Harris and MinimumEigenvalue ?? What method are you using ?? I would not recommend using the second method. It will not work well here as the image has more variations which will influence the Eigenvalue method's stability. So use the Harris's Corner detection method . Use the following ,

a = imread('door1.jpg');
b = a(:,:,1);
c = corner(b) % The default method used is Harris 
imshow(a);
hold on;
plot(c(:,1),c(:,2),'r*');