// Do the actual encryption of the message inside the picture.
procedure TForm1.btnEncryptClick(Sender: TObject);
 var
  x, y, i, j: Integer;
  PixelData: TColor;
  CharMask, CharData: Byte;
 begin
  // Assign the original picture to both the target encrypted image
 // and delta image. Also make sure thier resolution is sufficient to
 // indicate the change in the LSB.
 imgTarget.Picture.Assign(imgOrig.Picture);
  imgDelta.Picture.Assign(imgOrig.Picture);
  imgTarget.Picture.Bitmap.PixelFormat := pf32bit;
  imgDelta.Picture.Bitmap.PixelFormat := pf32bit;
  x := 0;
  y := 0;
  // The letter 'c' is identified by the binary representation of '10000011'
 // for each '1' in this number change the current pixel's LSB value.
 with imgTarget.Picture.Bitmap do
  for i := 1 to Length(sourceMessage.Text) do
  begin
  CharMask := $80;
  // 8 bytes for every letter to be encrypted.
  for j := 1 to 8 do
  begin
  // See if the current byte in the character is either '1' or '0'.
  CharData := Byte(sourceMessage.Text[i]) and CharMask;
  //Data is not zero - change the LSB of the current pixel.
  if (CharData <> 0) then
  begin
  // Xor the LSB value - hence change its value.
  PixelData := Canvas.Pixels[x, y] xor $1;
  // Store the changed pixel color back in the Pixels array.
  Canvas.Pixels[x, y] := PixelData;
  end;
  // Move to the next pixel.
  x := (x + 1) mod Width;
  if (x = 0) then
  begin
  Inc(y);
  end;
  // Move the mask to be applied to the current character to the
  // right, hence will now examine the next bit in the binary
  // representation of the current letter to be encrypted.
  CharMask := CharMask shr 1;
  end;
  end;
  // Show the difference in the Delta image.
 for y := 0 to imgOrig.Picture.Bitmap.Height -1 do
  for x := 0 to imgOrig.Picture.Bitmap.Width -1 do
  // Check for difference, the difference will show in the LSB of every
  // pixel in the original and target images.
  if (imgOrig.Picture.Bitmap.Canvas.Pixels[x, y] <>
  imgTarget.Picture.Bitmap.Canvas.Pixels[x, y]) then
  imgDelta.Picture.Bitmap.Canvas.Pixels[x, y] := clYellow;
 end;

 // Decryption ( by Lemy )
procedure TForm1.btnDecryptClick(Sender: TObject);
 Var
  x, y: integer;
  mask, ch: byte;
 begin
  sourceMessage.Clear;
  mask := $80;
  ch := 0;
  for y := 0 to imgOrig.Picture.Bitmap.Height -1 do
  begin
  for x := 0 to imgOrig.Picture.Bitmap.Width -1 do
  begin
  // if the pixel is different then set related bit
  if (imgOrig.Picture.Bitmap.Canvas.Pixels[x, y] <>
  imgTarget.Picture.Bitmap.Canvas.Pixels[x, y]) then
  ch := ch or mask;
  // shift the bit to the rigtht
  mask := mask shr 1;
  // if the mask is 0 then the dexryption of a char is completed
  // so add to the Text and rest the highest bit
  if mask = 0 Then
  begin
  sourceMessage.Text := sourceMessage.Text + char(ch);
  mask := $80;
  ch := 0;
  end;
  end;
  end;
 end;