It was a moving photo like countless others on Facebook, but the caption “four more years” said it all — US President Barack Obama had won re-election, and was about to make social media history.

After a months-long, gruelling presidential campaign fought both off- and online, Obama sealed his tech-savvy reputation late Tuesday by announcing his victory over Republican foe Mitt Romney on Twitter and Facebook with the photo.

By early Wednesday, the shot of a smiling Obama holding his wife Michelle in a loving embrace had already broken records on both social networks — bringing to a climax a hard-fought online campaign for supporters and votes.

“This Barack Obama photo is the most-liked Facebook photo of all time,” the social network announced Wednesday, as it clocked up more than 3.5 million “likes”.