This should do it
Sub center_image()
Dim osld As Slide
Dim oshp As Shape
Dim SW As Long
Dim SH As Long
SW = ActivePresentation.PageSetup.SlideWidth
SH = ActivePresentation.PageSetup.SlideHeight
For Each osld In ActivePresentation.Slides
For Each oshp In osld.Shapes
If isPic(oshp) Then
oshp.Left = SW / 2 - oshp.Width / 2
oshp.Top = SH / 2 - oshp.Height / 2
End If
Next oshp
Next osld
End Sub
Function isPic(oshp As Shape) As Boolean
If oshp.Type = msoPicture Then isPic = True
If oshp.Type = msoPlaceholder Then
If oshp.PlaceholderFormat.ContainedType = msoPicture Then
isPic = True
End If
End If
End Function