// 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;