conceal.m

function [key] = conceal()
tree = imread('tree.png');
tree = tree - mod(tree,4);%set least significant bits of each pixel color component to 00
r = tree(:,:,1);
g = tree(:,:,2);
b = tree(:,:,3);

key = randi(20);

hide(r,key,1);
hide(g,key,2);
hide(b,key,3);

result = tree;
result(:,:,1) = r;
result(:,:,2) = g;
result(:,:,3) = b;
imwrite(result, 'result.png');

end

function [hid] = hide(image,key,dim)
cat = imread('cat.png');
[row, col,~] = size(cat);
img = cat(:,:,dim);
% Unroll matrices to vectors to make them easy to loop over
treeVector = image(:);
catVector = img(:);
% Get the most significant bits
catVector = catVector./64;
max = row*col; % number of pixels/last index of vectors 
i = 1; % loop counter
temp = 2;
n = 1; % index
while(i<max)
    treeVector(n) = treeVector(n) + catVector(i);
    n = n + key;
    if n>max
        n = temp;
        temp = temp + 1;
    end
    i = i + 1;
end
hid = reshape(treeVector,[row,col]);
disp(hid);
end