How can I apply cropping attack for watermarking?

Question

When I apply crop attack on watermarked image it gives me a corrupted extracted watermark. Extracted watermark shows black at bottom of the corner but, it should not be black.

How can I solve this problem? How can I apply crop attack?

Watermarked image after crop attack

Extracted watermark

<I=double(imread('lena_gray_512.tif'));
W1=double(imread('cameraman256.gif'));

[cA1,cH1,cV1,cD1] = dwt2(I,'haar');
params=[0.03 0.30 0.01 0.01];
 for i=1:256
         for j=1:256
         IWA(i,j) =  cA1(i,j) + params(1) * W1(i,j);
        IWH(i,j) =  cH1(i,j) + params(2) * W1(i,j);
        IWV(i,j) =  cV1(i,j) + params(3) * W1(i,j);
        IWD(i,j) =  cD1(i,j) + params(4) * W1(i,j);
       end
    end
    IW=uint8(idwt2(IWA,IWH,IWV,IWD,'haar'));

[krp,rec]=imcrop(IW,[257 257 255 255]); 
krp(M1,N1)=0; 
tform = maketform('affine',[1 0 0; 0 1 0; rec(1,1)-1 rec(1,2)-1 1]); 
krp1= imtransform(krp,tform,'XData',[1 M1],'YData',[1 N1]);
IWD1=IW-krp1;

IWD1 = double(IWD1);
[cA1_IW,cH1_IW,cV1_IW,cD1_IW] = dwt2(IWD1,'haar');

for i=1:256
       for j=1:256     
        WA1(i,j) = (cA1_IW(i,j) - cA1(i,j)) / params(1);  
        WH1(i,j) = (cH1_IW(i,j) - cH1(i,j)) / params(2);
        WV1(i,j) = (cV1_IW(i,j) - cV1(i,j)) / params(3);
        WD1(i,j) = (cD1_IW(i,j) - cD1(i,j)) / params(4);
       end
    end

figure (4);
subplot(3,2,1); imshow(WA1,[]); title('WA5');
subplot(3,2,2); imshow(WH1,[]); title('WH5');
subplot(3,2,3); imshow(WV1,[]); title('WV5');
subplot(3,2,4); imshow(WD1,[]); title('WD5');