Or you could try NOTE This is a 1/4/ POINT border if you want 1/4 inch the weight value would be 18

Sub setPicType()
On Error Resume Next
If Err <> 0 Then Exit Sub
Dim osld As Slide
Dim oshp As Shape
For Each osld In ActivePresentation.Slides
For Each oshp In osld.Shapes
If IsPic(oshp) Then
' Grey adjust values to suit
oshp.Line.ForeColor.RGB = RGB(200, 200, 200)
oshp.Line.Weight = 0.25
End If
Next
Next
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 Function