A file container for storing two lossless images?

I am scanning my card collection, and for each card I’m scanning the front and back. Now I’m looking for a file container that can store them into one single file, and this file should also be able to read by image viewer with thumbnail.

What are my options for this? The first thing that comes to mind is pdf, but I don’t think it stores lossless images like png. A zip is able to store lossless but it couldn’t be read by image viewer and no thumbnails on Windows.