如何在C＃中将图像从Power point复制到剪贴板

Question

我使用以下代码将图像从PowerPoint保存到本地磁盘：

var shape = presentation.Slides[1].Shapes[1];   
shape.Copy(); //copy a shape from a slide to clipboard          
bool imgOk = Clipboard.ContainsImage(); //check if copied shape is an image

if (imgOk)
{
       Console.WriteLine(imgOk.ToString());
       Image img = Clipboard.GetImage();                   
       string filepath = @"D:\Peak Sourcing\Work\ppt_test\img.jpg";                    
       img.Save(filepath);
}

ppt中只有一张幻灯片有一张图片。但图片不会被复制到剪贴板。怎么解决这个问题？