How to make the image appear when sharing a webpage?


I am using a CNN article page as an example:

In the webpage html head there is this tag:

<meta name="twitter:image" content="">

But when I click on twitter share button to share the page, all i see is:

“The best blood test you’ll ever take via @CNNMoney

Even if I log into twitter and shared the page, I still don’t see
that image! What is wrong? I am trying to do this for my website.

I would think CNN, one of the biggest news
site in the world, have already gotten approval from twitter and yet still not
working. In fact, I have never seen a working “twitter card” with image being
shared on any webpage, any website.

Can someone please provide a working example on any website?