I have implemented summary_large_image cards and gone through to below simple steps
as you mention in doc .but no any card is appears on sharing .
and when i checked page source it shows all meta tag as you mention in summary_large_image cards doc . but noting happens when sharing only link is shared image not comes.
page source url:
Get started in 5 simple steps
Ready to get started with Cards? In most cases, it takes less than 15 minutes to implement.
Choose a card type you want to implement.
Add the pertinent meta tags to your page.
Run your URL against the validator tool to test. If you are working with a Player Card, request approval for whitelisting. All other Cards do not need whitelisting.
After testing in the validator or approval of your Player Card, Tweet the URL and see the Card appear below your tweet in the details view.
Use Twitter Card analytics to measure your results.
can you short out this problem.