LSB steganography : i can't extract the original messages

the code is:

embedding code:

c = imread('lena.jpg');
    message = 'hellokarthick';
    message = strtrim(message);
    m = length(message) * 8;
    AsciiCode = uint8(message); 
    binaryString = transpose(dec2bin(AsciiCode,8));
    binaryString = binaryString(:);
    N = length(binaryString);
    b = zeros(N,1); %b is a vector of bits
    for k = 1:N
        if(binaryString(k) == '1')
            b(k) = 1;
        else
            b(k) = 0;
        end
    end
    s = c;
    height = size(c,1);
    width = size(c,2);
    k = 1;
    for i = 1 : height
        for j = 1 : width
             LSB = mod(double(c(i,j)), 2);
            if (k>m || LSB == b(k))
                s(i,j) = c(i,j);
                else
                    s(i,j) = c(i,j) + b(k);
            k = k + 1;
        end
        end
    end
     imwrite(s, '111.jpg');

Extraction:

    for i = 1 : height
        for j = 1 : width
            if (k <= m)
                b(k) = mod(double(s(i,j)),2);
                k = k + 1;
            end
        end
    end
    binaryVector = b;
    binValues = [ 128 64 32 16 8 4 2 1 ];
    binaryVector = binaryVector(:);
    if mod(length(binaryVector),8) ~= 0
        error('Length of binary vector must be a multiple of 8.');
    end
    binMatrix = reshape(binaryVector,8,100);
    display(binMatrix);
    textString = char(binValues*binMatrix);    
    disp(textString);

The output is:

Answer 1

[Geoff Hayes]

Arjun - I suspect the problem is with the line

imwrite(s, '111.jpg');

You are saving s, the image with the secret message, as a jpeg which is a lossy compression method. This means that you are most likely losing information when you save s in this manner. You can prove this by comparing s with that data which is returned by

 sp = imread('111.jpg');

s and sp are most likely not identical and so the LSB extraction method (from above) will fail.

I think that you can do one of two things - save the image as bitmap or set the compression to none as

 imwrite(s,'111.jpg','Compression','none');

Try the above and see what happens!

[Walter Roberson]

Yup.

More advanced steganography mimics the way that JPEG compresses files and embeds the data in the compression coefficients and then transforms back. In this way the image produced will survive JPEG compression, provided that the Quality factor is not set lower than is accounted for.

To be robust, you need to hide a bit stream that has redundancy so that it can be reconstructed if it gets corrupted. Error Correcting Codes (ECC) are used for this purpose. See Forward Error Correction.

Good steganography accounts for the possibility of the image being resized, and accounts for possibilities like the image to be decoded being a photograph (or screen capture) of the image that has the hidden information.

[ARJUN K P]

its not working... its error...

[ARJUN K P]

i also try with .bmp format... i extracted text is unreadable...

[Walter Roberson]

Use 'mode', 'lossless' on the imwrite() instead of 'Compression', 'none'.