We are running into situations where the DB record of a page is present, but the actual image is not. 

After some digging around, we found that the code below works well and quickly:

            Dim LF_PageInfo As PageInfoReader = LF_DocInfo.GetPageInfos
            Dim LF_PageSet As Laserfiche.RepositoryAccess.PageSet = New PageSet
            Dim ms As LaserficheReadStream
            Dim LF_PP As PagePart = New PagePart

            For Each PageInfo In LF_PageInfo
                'Try to read each page
                ms = PageInfo.ReadPagePart(LF_PP)
                'Evaluate
                If ms.Length > 0 Then
                    'If OK, add it to the PageSet
                    LF_PageSet.AddPage(PageInfo.PageNumber)
                End If
            Next

            'Make sure we have something to export
            If LF_PageSet.GetTotalPageCount > 0 Then

                'Set the Exporter Properties
                LF_DocExporter.IncludeAnnotations = False
                LF_DocExporter.BlackoutRedactions = False

                'Export the document
                LF_DocExporter.ExportPdf(LF_DocInfo, LF_PageSet, _
                         PdfExportOptions.None, sExportPath)
           End If

Note that this does not help with the situation where the image is present but corrupt.