There are a couple of options, any of which could be the "best practice" for your scenario.
Probably the easiest method would be to convert each image to a PDF with Convert.ToPDF():
http://www.pdftron.com/pdfnet/samplecode.html#ConvertYou could then combine the PDFs together, as demonstrated in the PDFPage sample:
http://www.pdftron.com/pdfnet/samplecode.html#PDFPageand then you could convert the result to Xod with Convert.ToXod().
Alternately, you could compose a single PDFDoc containing the images by placing them onto PDF pages, as shown by the AddImage sample:
http://www.pdftron.com/pdfnet/samplecode.html#AddImageThen you could convert the PDFDoc to Xod with Convert.ToXod().
If you have some image processing software, you could merge the images into a single multi-page TIFF, then convert directly to Xod.