resizing the image in PPT using VBA

Can someone please help?

Hi, this maximises all images in the presentation.

Public Sub MaximiseImages()
    Dim p As Presentation
    Set p = ActivePresentation
    Dim HeightMax As Single, WidthMax As Single
    HeightMax = p.SlideMaster.Height
    WidthMax = p.SlideMaster.Width
    Dim s As Slide
    For Each s In p.Slides
        Dim i As Shape
        For Each i In s.Shapes
            If i.Type = msoPicture Then
                i.LockAspectRatio = msoFalse
                i.Top = 0
                i.Height = HeightMax
                i.Left = 0
                i.Width = WidthMax
            End If
        Next i
    Next s
End Sub

How did you define SlideMaster as in the above code?