Image Watermarking Using DCT

Hello im new to mathlab and doing image watermarking using dct method, but im facing this problem can anyone help me:( im a very beginner:(

clc;
clear all

I=imread('Sunset.jpg'); I=imresize(I,[300 300]);
if size(I,3)==3
    I=rgb2gray(I);
end
figure,imshow(I), title('CITRA Penampung')

W=imread('copyright1.png'); I=imresize(W,[300 300]);
if size(W,3)==3
    W=rgb2gray(W);
end
figure,imshow(W), title('CITRA Watermark')

alpha = 0.02;
A = dct2(double(I));
B = dct2(double(W));
C = A + alpha*B;
Iw = round(real(idct2(C)));
IIw = uint8(Iw)
figure,imshow(IIw), title('CITRA Terwatermark')

I=imread('Sunset.jpg'); I=imresize(I,[300 300]);
if size(I,3)==3
    I=rgb2gray(I);
end
A=dct2(double(I));
C1=dct2(double(Iw));
B1=(C1-A)./alpha;
W1=uint8(idct2(B1));
figure,imshow(W1), title('CITRA Watermark Hasil Ekstraksi')

%this is the error I get
Matrix dimensions must agree.

Error in dct (line 76)
  b = W .* fft(y);

Error in dct2 (line 49)
    b = dct(dct(arg1).').';

Error in dctcoba (line 17)
A = dct2(double(I));

[Walter Roberson]

Put in a breakpoint at the beginning of the assignment to A and run the code. What shows up for size(A)?

[Cua Domain]

did you solve this? please help me

[Walter Roberson]

Cua, if you are encountering this problem, please show us size() of what you pass to dct2