text: Revenue sources On April 13, 2010, Twitter announced plans to offer paid advertising for companies that would be able to purchase "promoted tweets" to appear in selective search results on the Twitter website, similar to Google Adwords' advertising model. Users' photos can generate royalty-free revenue for Twitter, and an agreement with World Entertainment News Network (WENN) was announced in May 2011. Twitter generated an estimated US$139.5 million in advertising sales during 2011.
  In June 2011, Twitter announced that it would offer small businesses a self-service advertising system. The self-service advertising platform was launched in March 2012 to American Express card members and merchants in the U.S. on an invite-only basis. To continue their advertising campaign, Twitter announced on March 20, 2012, that promoted tweets would be introduced to mobile devices. In April 2013, Twitter announced that its Twitter Ads self-service platform, consisting of promoted tweets and promoted accounts, was available to all U.S. users without an invite.
  On August 3, 2016, Twitter launched Instant Unlock Card, a new feature that encourages people to tweet about a brand in order to earn rewards and utilize the social media network's conversational ads. The format itself consists of images or videos with call-to-action buttons and a customizable hashtag.