A combination photo shows U.S. President Barack Obama on April 29, 2009 (top) and on May 15, 2013. Obama's hair has become visibly greyer since he was first sworn into office on January 20, 2009 as a 47-year-old. Now, over four years into a presidency which has been marked by issues including bitter partisan struggles in Washington, a sluggish economy and the ongoing war in Afghanistan, his hair is noticeably more flecked with white. Obama has joked about his changing hair, including at the annual White House Correspondents' Association dinner on April 27, 2013 when he commented: "Time passes. You get a little grey." REUTERS/Larry Downing (top) and Kevin Lamarque/Files (UNITED STATES - Tags: POLITICS HEADSHOT)