image comparison

Question

hello,
        i want to compare two  image and difference should be saved in another image file. i am using c#.net.
i have write the following code to compare two bitmap file but when i try to compare images from my harddisk it does not show correct output.
i use following statement to use my image stored on harddisk. 
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
ServiceReference1.Service1SoapClient f = new ServiceReference1.Service1SoapClient();
label1.Text= f.HelloWorld();
Bitmap image1 = new Bitmap(400, 400);
using (Graphics g = Graphics.FromImage(image1))
{
g.DrawRectangle(Pens.Blue, new Rectangle(0, 0, 60, 60));
g.DrawRectangle(Pens.Red, new Rectangle(0, 0, 100, 100));
}
image1.Save("D:\\test-1.Jpeg", ImageFormat.Jpeg);
Bitmap image2 = (Bitmap)image1.Clone();
using (Graphics g = Graphics.FromImage(image2))
{
g.DrawRectangle(Pens.Purple, new Rectangle(0, 0, 100, 100));
}
image2.Save("D:\\test-2.Jpeg", ImageFormat.Jpeg);
Bitmap diff = ImageTool.GetDifferenceImage(image1, image2, Color.Pink);
diff.MakeTransparent(Color.Pink);
diff.Save("D:\\test-diff.bmp", ImageFormat.Bmp);

}
public class ImageTool
{
public static unsafe Bitmap GetDifferenceImage(Bitmap image1, Bitmap image2, Color matchColor)
{
if (image1 == null | image2 == null)
return null;
if (image1.Height != image2.Height || image1.Width != image2.Width)
return null;
Bitmap diffImage = image2.Clone() as Bitmap;
int height = image1.Height;
int width = image1.Width;
BitmapData data1 = image1.LockBits(new Rectangle(0, 0, width, height),
ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
BitmapData data2 = image2.LockBits(new Rectangle(0, 0, width, height),
ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
BitmapData diffData = diffImage.LockBits(new Rectangle(0, 0, width, height),
ImageLockMode.WriteOnly, PixelFormat.Format24bppRgb);
byte* data1Ptr = (byte*)data1.Scan0;
byte* data2Ptr = (byte*)data2.Scan0;
byte* diffPtr = (byte*)diffData.Scan0;
byte[] swapColor = new byte[3];
swapColor[0] = matchColor.B;
swapColor[1] = matchColor.G;
swapColor[2] = matchColor.R;
int rowPadding = data1.Stride - (image1.Width * 3);
// iterate over height (rows)
for (int i = 0; i < height; i++)
{
// iterate over width (columns)
for (int j = 0; j < width; j++)
{
int same = 0;
byte[] tmp = new byte[3];
// compare pixels and copy new values into temporary array
for (int x = 0; x < 3; x++)
{
tmp[x] = data2Ptr[0];
if (data1Ptr[0] == data2Ptr[0])
{
same++;

}

data1Ptr++; // advance image1 ptr
data2Ptr++; // advance image2 ptr
}
// swap color or add new values
for (int x = 0; x < 3; x++)
{
diffPtr[0] = (same == 3) ? matchColor.G : tmp[x];//swapColor[x] : tmp[x];
diffPtr++; // advance diff image ptr
}
}
// at the end of each column, skip extra padding
if (rowPadding > 0)
{
data1Ptr += rowPadding;
data2Ptr += rowPadding;
diffPtr += rowPadding;
}
}
image1.UnlockBits(data1);
image2.UnlockBits(data2);
diffImage.UnlockBits(diffData);
return diffImage;
}
}
}
 
would anyone help me out.
thanks in advance