I use PSO to get watermarking scaling factor.( the intensity factor)

wt=image + watermark * scaling factor

this is my fitness function: f(x)=(corr2(A,Aw)+corr2(w,we)/2)

where, A and Aw are cover and watermarked image respectively and W and We are original and extracted watermark respectively. Fitness function value range is from 0 to 1.

and this is my code in matlab for this function:

val=(corr2(image1,watermarked_image2)+corr2(img2,img3)/2.0);

I don't know whether my code is right or no? I attached  the article and my m.file.