Twitter Cards is the microblogging service’s push into creating a more media-centric experience for users. It allows publishers and third-party applications to display photos, video and article text inside of tweets, rather than only sharing links inside of tweets.
“Instagram has disabled photo integration with Twitter. As a result, photos are no longer appearing in Tweets or user photo galleries. While tweeting links to Instagram photos is still possible, you can no longer view the photos on Twitter, as was previously the case.”