First you should avoid using bit.ly, Twitter already has t.co url shortener so no need for it. (If you just did it for this forum, ignore what I said)
Second, what I get when I impersonate Twitterbot is the following:
<!doctype html>
<html lang="en">
<meta charset="utf-8">
<title>Kanvz Inc.</title>
<meta name="twitter:site" content="Kanvz Inc." />
<meta name="twitter:creator" content="T. R. Ramachandran" />
<meta name="twitter:title" content="Gun-Deaths and Mass Shootings in the US" />
<meta name="twitter:description" content="1) In the wake of the terrible #uccshooting in Oregon today, it's worth looking at some of the shocking stats on gun-related deaths in the US.
We can start with the Washington Post and the Mass Shooting Tracker. " />
<meta name="twitter:card" content="photo" />
<meta name="twitter:image" content="https://img.washingtonpost.com/blogs/wonkblog/files/2015/10/mass_shootings.png" />
<meta name="twitter:url" content="http://www.kanvz.com" />
<h1>embed-photo</h1>
This is completely wrong, not even the basic html structure is right. That’s how it should look like:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Kanvz Inc.</title>
<!-- The twitter:site tag must indicate a Twitter @username, not any name. -->
<meta name="twitter:site" content="@KanvzInc">
<!-- Twitter card type -->
<meta name="twitter:card" content="summary_large_image">
<!-- The twitter:creator must indicate a Twitter @username, not any name. -->
<!-- If the user has no Twitter, omit this tag! -->
<!-- <meta name="twitter:creator" content="@someone"> -->
<!-- Twitter card title -->
<meta name="twitter:title" content="Gun-Deaths and Mass Shootings in the US">
<!-- Twitter card description -->
<meta name="twitter:description" content="1) In the wake of the terrible #uccshooting in Oregon today, it's worth looking at some of the shocking stats on gun-related deaths in the US.
We can start with the Washington Post and the Mass Shooting Tracker. ">
<!-- Twitter card image -->
<meta name="twitter:image" content="https://img.washingtonpost.com/blogs/wonkblog/files/2015/10/mass_shootings.png">
</head>
<body>
<h1>embed-photo</h1>
</body>
</html>