DCT code for image hash

I am working on a project to assign fingerprint to images using pHash. I happened to get the following code from StackOverflow:

% read image
I = imread('cameraman.tif');

% cosine transform and reduction
d = dct2(I);
d = d(1:8,1:8);

% compute average
a = mean(mean(d));

% set bits, here unclear whether > or >= shall be used
b = d > a;
% maybe convert to string:
string = num2str(b(:)');

When I run the code, I get the following errors, all of which are associated with built-in functions:

Matrix dimensions must agree.

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

Error in dct2 (line 50)
    b = dct(dct(arg1).').';

Error in flipimage (line 4)
d = dct2(I);

Please help me to resolve these errors

Answer 1

[Abhishek Ballaney]

https://www.mathworks.com/help/images/ref/dct2.html