Entropy and Correlation -Image analysis

Hi I implemented data hiding in image and now i want to determine the extent to which the original image and the stego-image are close to each other

PSNR and MSE parameters can be used for the same which I have implemented for looking for matlab code on following performance measurement parameters

Entropy  
Correlation = RXY (α,β )= ∑i ∑j X(i,y) Y(i-α ,j- β) 
I am using grayscale image for implementation. Any help appreciated

For Entropy, is following code correct?

I=imread(" orginal image name")     
J=Entropy(I)        
K=imread(" Stego image name")     
M=Entropy(K) 

In Ideal case diffrence between J &M should be zero

[Nil]

Anyone pls help me out