Services based on Apple Passbook usually provide users with a PDF variant in confirmation e-mails, as well as the possibility to print additional PDF tickets from the users account. Once you have the .pdf file it's pretty easy to get it printed as PNG image using any of the available pdf to png conversion options.
Worth mentioning is the fact that .pkpass files are basically renamed ZIP archives. Any file archiver can extract the contents and you may find a thumbnail preview of the ticket in one of the subfolders.
Open PKPASS file Open PNG file