ROUGH CUT (NO REPORTER NARRATION)
STORY: G20 leaders pose for a group photo to mark the first day of the summit of world economic powers.
Fast-moving events in Greece overshadowed the first day of the summit on the French Riviera, with world leaders anxiously urging Europe to take decisive action to halt its sovereign debt crisis.
Greece's teetering government backed away from a proposed referendum on staying in the euro on Thursday, while European leaders talked for the first time of a possible Greek exit to preserve the single currency.