How to crop an image using C#?

Check out this link: http://www.switchonthecode.com/tutorials/csharp-tutorial-image-editing-saving-cropping-and-resizing

private static Image cropImage(Image img, Rectangle cropArea)
{
   Bitmap bmpImage = new Bitmap(img);
   return bmpImage.Clone(cropArea, bmpImage.PixelFormat);
}

You can use Graphics.DrawImage to draw a cropped image onto the graphics object from a bitmap.

Rectangle cropRect = new Rectangle(...);
Bitmap src = Image.FromFile(fileName) as Bitmap;
Bitmap target = new Bitmap(cropRect.Width, cropRect.Height);

using(Graphics g = Graphics.FromImage(target))
{
   g.DrawImage(src, new Rectangle(0, 0, target.Width, target.Height), 
                    cropRect,                        
                    GraphicsUnit.Pixel);
}

Simpler than the accepted answer is this:

public static Bitmap cropAtRect(this Bitmap b, Rectangle r)
{
    Bitmap nb = new Bitmap(r.Width, r.Height);
    using (Graphics g = Graphics.FromImage(nb))
    {
        g.DrawImage(b, -r.X, -r.Y);
        return nb;
    }
}

and it avoids the "Out of memory" exception risk of the simplest answer.

Note that Bitmap and Graphics are IDisposable hence the using clauses.

EDIT: I find this is fine with PNGs saved by Bitmap.Save or Paint.exe, but fails with PNGs saved by e.g. Paint Shop Pro 6 - the content is displaced. Addition of GraphicsUnit.Pixel gives a different wrong result. Perhaps just these failing PNGs are faulty.