any samples for c# windows form passport size photo image background changer

Bitmap bitmap

 for (int y = 0; y < bitmap.Height; y++)
            {
               for (int x = 0; x < bitmap.Width; x++)
              {
                  Color pixelColor = bitmap.GetPixel(x, y);                    
                       bitmap.SetPixel(x, y, color);

               }
            }
           return bitmap;