C#-FORM : Using GetHashCode() to compare files.

[ds81]

I am trying to read a large number of image (BMP, JPG) files, and need to know if any are identical. I have been trying to store the hashcodes of the files, so that they then can be compared later.

But this function...

        private void imageHash(string filename)
        {
            FileStream fs = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.None);
            Image image = Image.FromStream(fs);
            Int32 imagehash = image.GetHashCode();            
            MessageBox.Show(imagehash.ToString());            
            fs.Close();
            fs.Dispose();            
        }
 

...seems to return different values when the same filename is supplied.

What am I doing wrong?