How to find angle of rotation between two images

Hi I'm using matlab to try and detect the angle by which the rectangles are inclined in the image. The code I used so far is below. I need to find the rotation between two images so I tried rotating one image and comparing it with the other image but that doesn't work as the image dimensions change on rotating. I know I need to use hough transform but can't figure out how. I have attached the three images i am using as lhs.jpg, center.jpg and rhs.jpg depending on the view the picture has been taken from.

http://imageshack.us/photo/my-images/94/rhsq.jpg/

clc;
clear all;
%%Procedure for RHS

I = imread('rhs.jpg');

% creating RGB matrices and storing dimensions
R = I(:,:,1);
G = I(:,:,2);
B = I(:,:,3);
size = size(R);
rows = size(1,1);
columns = size(1,2);

% Manipulating pixels
for i = 1:rows
    for j = 1:columns
         if B(i,j) <= 70;
            I(i,j,:) = 255;
        end
    end
end
figure, imshow(I)

%edge detection
I = rgb2gray(I);
I = imadjust(I, [0.3 0.9], [0 1]);
BW1 = edge(I,'canny',0.15);
figure, imshow(BW1);
[H,theta,rho] = hough(BW1);
% figure, imshow(imadjust(mat2gray(H)),[],'XData',theta,'YData',rho,...
%         'InitialMagnification','fit');
xlabel('\theta (degrees)'), ylabel('\rho');
axis on, axis normal, hold on;
colormap(hot)
P = houghpeaks(H,75,'threshold',ceil(0.11*max(H(:))));
lines = houghlines(BW1,theta,rho,P,'FillGap',5,'MinLength',5);
figure, imshow(BW1), hold on
max_len = 0;
for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   plot(xy(:,1),xy(:,2),'LineWidth',3,'Color','green');
end

%%Procedure for LHS

clear I;
clear R;
clear G;
clear B;
clear size;

I = imread('lhs.jpg');

% creating RGB matrices and storing dimensions
R = I(:,:,1);
G = I(:,:,2);
B = I(:,:,3);
size = size(R);
rows = size(1,1);
columns = size(1,2);

% Manipulating pixels
for i = 1:rows
    for j = 1:columns
         if B(i,j) <= 70;
            I(i,j,:) = 255;
        end
    end
end
figure, imshow(I)

%edge detection
I = rgb2gray(I);
I = imadjust(I, [0.3 0.9], [0 1]);
BW2 = edge(I,'canny',0.15);
figure, imshow(BW2);
[H,theta,rho] = hough(BW2);
% figure, imshow(imadjust(mat2gray(H)),[],'XData',theta,'YData',rho,...
%         'InitialMagnification','fit');
xlabel('\theta (degrees)'), ylabel('\rho');
axis on, axis normal, hold on;
colormap(hot)
P = houghpeaks(H,75,'threshold',ceil(0.11*max(H(:))));
lines = houghlines(BW2,theta,rho,P,'FillGap',5,'MinLength',5);
figure, imshow(BW2), hold on
max_len = 0;
for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   plot(xy(:,1),xy(:,2),'LineWidth',3,'Color','green');
end

%%Finding angle of rotation by rotating by trial and error angles

diff = BW1 - BW2;
for i = 1:180
    BW1 = imrotate(BW1,i);
    newdiff = BW1-BW2;
    if newdiff < diff
        diff = newdiff;
        angle = i;
    end
end

Answer 1

[Sean de Wolski]

doc imregister

[Karan]

How do you suggest using it? Also it doesn't show up on the product help

[Sean de Wolski]

It was introduced in R2012a.

[Karan]

I'm using 2011. Suggestions based on that please.

Answer 2

[Sharvil]

Heyy..This code is perfect but it shows an error in the last if condidion that : "Matrix dimensions must be same" Can you please resolve this error?