How to crop the right position of element from the screen shot?

Currently i am working on a selenium webdriver tool. This tool is going to screen shot a website page and crop it into the size of the element i look for. However, I am not able to get the correct coordinates all of the time. I tried to get the element location, determined its height and width but still it return me the wrong answer and wrong cropped image. Any idea ?

Code:

IWebElement img = driver.FindElement(By.Id("IMG1"));
int width = img.Size.Width;
int height = img.Size.Height;
Point point = img.Location;
int x = point.Location.X;;
int y = point.Location.Y;
RectangleF part = new RectangleF(x, y, width, height);
Bitmap bmpobj = new Bitmap(filePath);
Bitmap bn = bmpobj.Clone(part, bmpobj.PixelFormat);

Above is the code i used to get the location of the element and crop. Any one check for me any wrong with this?

PS: The website i tried to screen capture contain an iframe content which load a long page with scroll bar. Is that possible the location of the image is far too down causing me unable to get the right coordinate after all?

adviser... need help please... what is the problem that i cant get the correct position of the image that i wanted to crop?