gistfile1.bas

'Erase alt text of images from pptx
Option Explicit

Private Sub delAlt(sh As Shape)
    Dim s As Shape

    sh.AlternativeText = ""
    On Error GoTo trap
    For Each s In sh.GroupItems
        Call delAlt(s)
    Next
trap:
    Err.Clear
End Sub

Public Sub test()
    Dim a As Presentation
    Dim sd As Slide
    Dim sh As Shape

    For Each sd In Presentations(1).Slides
        For Each sh In sd.Shapes
            Call delAlt(sh)
        Next
    Next

End Sub