• by Laurie Sullivan  @lauriesullivan, June 21, 2012

Every image tells a story on television, but not a complete picture without real-time tweets connecting TV with online, says Twitter CEO Dick Costolo, speaking at Cannes Lions.

The biggest challenge, it seems, is that broadcast TV needs a dependable partner -- but by Thursday the added tweet volume from the ad festival appears to have sent the site offline.

Earlier in the week, the site boasted that there were more than 15,000 online posts across social media referencing #CannesLions, with 95% coming from Twitter. On Thursday, as of 12:40 EST, the site went offline. Remember #failwhale? Broadcast TV needs a reliable social media partner.

While it all began with lower thirds serving up at the bottom of TV screens during broadcasts, Twitter pushed the concept of using the site to bring TV viewers online and connect them with other socialites to create a community in real-time. A producer's guide explaining best practices for connecting TV audience through tweets went up on the Twitter's site in early June.

TV shows have tapped the social site to raise ratings. The company developed an analytics package to track the continuous tweets during television broadcasts. The sharp spikes correspond to major moments in a show.

Last year, Twitter and technology partners stepped up following tweets to TV, bringing real-time content to TV shows. But the interaction between viewers and TV content presents another dynamic that makes the big screen more relevant to marketers.

Costolo also said Twitter would begin offering promoted advertising in 50 additional markets this year, reducing its reliance on revenue from the U.S.

Twitter's worldwide ad revenue should rise 86.3% to nearly $260 million -- up from $139 million in 2011 -- and $45 million in 2010, eMarketer estimates. About 90% of Twitter's revenue comes from the United States, but this year, $26 million in ad revenue could come from overseas, the research firm said.

Earlier this week, Twitter introduced Cards, making it possible to attach media to tweets that link to content through a few lines of HTML code on the Web site. A "Card" is added when site visitors tweet links to the content. It automatically attributes content to the site. There are three types of Cards: summary, photo and player.