Sub InsertAndSizePicture()

    Dim oPicture As Shape
    Dim FullPath As String
    Dim oSl As Slide

    ' Set this to the full path to picture.
    FullPath = "C:\My Documents\Pictures\MyPhoto.JPG"

    Set oSl = ActiveWindow.Selection.SlideRange(1)

    ' Insert the picture at an arbitrary size;
    ' PowerPoint requires you to supply *some* height and width for the picture
    Set oPicture = oSl.Shapes.AddPicture(FileName:=FullPath, _
       LinkToFile:=msoFalse, _
       SaveWithDocument:=msoTrue, _
       Left:=0, Top:=0, _
       width:=100, height:=100)

    ' Rescale the picture to its "natural" slze
    With oPicture
       .Scaleheight 1, msoTrue
       .Scalewidth 1, msoTrue
    End With

    Set oPicture = Nothing
    Set oSl = Nothing

End Sub