为什么word中图片拷贝后再剪切板中读取不到，求大神解答一下

        For Each item As Paragraph In WordDoc.Paragraphs
            If item IsNot Nothing Then
                If item.Range.Text.Trim() <> "" Then
                    If item.Range.InlineShapes.Count <> 0 Then
                        Dim imgname As Integer = 0
                        For Each shape As InlineShape In item.Range.InlineShapes
                            If shape.Type = WdInlineShapeType.wdInlineShapePicture Then
                                shape.Select()
                                WordApp.Selection.CopyAsPicture()
                                If Clipboard.ContainsImage() Then
                                    Dim bmp As Bitmap = New Bitmap(Clipboard.GetImage())
                                    imgname = imgname + 1
                                    bmp.Save("C:\SHH\TMP" + temp + ".png", System.Drawing.Imaging.ImageFormat.Png)
                                End If
                            End If
                        Next
                    End If
                End If

            End If

                            ，为什么Clipboard.ContainsImage()一直返回false

Clipboard.ContainsImage()不能识别png