This should work though not thoroughly tested!
MAKE SURE YOU WORK ON A COPY!
Code:
Sub picPres()
Dim osld As Slide
For Each osld In ActivePresentation.Slides
ActiveWindow.View.GotoSlide osld.SlideIndex
With osld.Shapes.AddShape(msoShapeRectangle, 0, 0, ActivePresentation.PageSetup.SlideWidth, ActivePresentation.PageSetup.SlideHeight)
.Fill.Visible = False
.Line.Visible = False
End With
osld.Shapes.Range.Cut
With osld.Shapes.PasteSpecial(ppPastePNG)
.Left = 0
.Top = 0
.Width = ActivePresentation.PageSetup.SlideWidth
End With
osld.Layout = ppLayoutBlank
Next
End Sub