function psnr = psnr(Watermark,AttackedWatermark)
x=Watermark;
y=AttackedWatermark;

if x== y
   error('Images are identical: PSNR has infinite value')
end
x=double(x(:,:,1));
y=double(y(:,:,1));
d = mean( mean( (x(:)-y(:)).^2 ) );
m1 = max( abs(x(:)) );
m2 = max( abs(y(:)) );
m = max(m1,m2);

psnr = 10*log10( m^2/d );