Will social media decide the US presidential election?

Embracing social media was an important part of Barack Obama's successful 2008 campaign. And according to analysts, the president still has an edge over his Republican opponents in this regard four years on.

But it is no longer enough to just target Facebook users.

The technology has changed dramatically, with Twitter now a key part of any political campaign and micro-blogging sites like Tumblr offering new ways to reach voters with messages tailored to individuals.

The BBC's Matt Danzico looks at the ways in which both candidates are trying to use social media to enthuse supporters and sway undecided voters.