Sub TogglePicture()
Dim oRng As Range
Dim oShape As InlineShape
    Set oRng = ActiveDocument.Tables(1).Cell(4, 2).Range
    With oRng.InlineShapes(1)
        If .PictureFormat.Brightness = 1 Then
            .PictureFormat.Brightness = 0.5
        Else
            .PictureFormat.Brightness = 1
        End If
    End With
End Sub