Excluding white squares from a scrambled image

Hi There,

So I have a piece of code which should chop up squares of an image and scramble them. I have a series of faces which are on a white background. What I am trying to do is take a random square from a random image to add to a final scrambled image, but not if that square is white.

This is the code:

%% first getting the size of the image and dividing it into blocks of 30 pixels

n = 30;
image_size = imread(all_images{1});
mn = floor(size(image_size)/n);
m1 = mn(1);
n1 = mn(2);

% a new matrix for the scrambled blocks to go in

newim = zeros(m1*n,n1*n);

% there are 51 images in the file

for bb = 1:51   
for k = 1:m1*n1

     good_squares = false;
     while ~good_squares

current_image = randsample(1:51, 1);
my_image = imread(all_images{current_image});

ind = randperm(m1*n1);
[ind1, ind2] = ind2sub([m1, n1], ind);
[i,j]=ind2sub([m1, n1], k);

newim((i-1)*n+1:i*n, (j-1)*n+1:j*n) = ...
my_image((ind1(k)-1)*n+1:ind1(k)*n,(ind2(k)-1)*n+1:ind2(k)*n);

x = my_image((ind1(k)-1)*n+1:ind1(k)*n,(ind2(k)-1)*n+1:ind2(k)*n);

good_squares = true;

       if x(1, 1) == 255 && x(1, 30) == 255 && x(30, 1) == 255 
           good_squares = false;
       elseif x(1, 1) == 255 && x(1, 30) == 255 && x(30, 30) == 255
           good_squares = false;
       elseif x(30, 1) == 255 && x(30, 30) == 255 && x(1, 30) == 255
           good_squares = false;
       end

      end

end

%   write out new mask
         imwrite(newim, ['mask' num2str(bb) '.bmp'],'bmp');

end

So where I run the exclusion portion of the code (good_blocks = false) I am trying to exclude a block if the pixels in three of the corners are white. This code spits out 51 pure white images, so either the indexing is broken, or the while loop is not right. Any suggestions on how to do this is appreciated.