Private Sub PageHeaderSection_Format(Cancel As Integer, FormatCount As Integer)
If FormatCount = 1 Then
If Me.Page Mod 2 = 1 Then
Me.Picture = "C:\Path\To\Image\FirstImage.bmp"
Else
Me.Picture = "C:\Path\To\Image\SecondImage.bmp"
End If
End If
End Sub
So that example shows FirstImage.bmp if the page is an odd number and SecondImage.bmp for even page numbers. Note that it uses the Format event of the Page Header section.
You can use a SELECT CASE statement if you want to apply different criteria, but you get the gist of it.