Need help in following code snippet

I am trying to call a static function cropImage here is how it looks..

 public static Image CropImage(Image img, Rectangle cropArea)
 {
        logic goes here..
 }

I want to call this function to crop am i开发者_运维百科mage how can I do this? When I tried like this

Rectangle objRect=new Rectangle(20,10,200,100);
static_className.CropImage(image,objRect);

I got an error saying invalid argument.

Image oldImg;

Rectangle objrect=new Rectangle(20,10,200,100);
Image newImage=static_className.cropImage(oldImg,objrect);