It's possibly the most memorable first kiss in history.

Most of the young students at Daughter of Zion Junior Academy in Florida understandably thought US President Barack Obama was the most interesting thing in the room as he sat down to pose for a surprise group photo yesterday.

But for a boy in the back row, it was the girl next to him that really caught his eye.

He was snapped enthusiastically kissing her on the cheek, with his hands clasped affectionately around her neck and face.

The picture, posted on the President's Twitter account as "photo of the day", has been retweeted nearly 2000 times and "favourited" by over 1000 people.

The students had lined up to wave as his motorcade passed their school, but the President decided to make an unscheduled stop.

It's not the only time a candidate has been "photobombed" on the campaign trail.

An excited worker made headlines around the world when he posed with Mitt Romney at the Chipotle restaurant in Denver on October 2.

Most of the employees he greeted appeared quite pleased to be posing with the Republican candidate, but Marty Arps seemed ecstatic, grinning with wide eyes and pointing at Mr Romney.

Mr Arps later explained that he made the alarming expression when he was excited.

"I [did that] when I met Nicki Minaj. It's like, 'Ah, it's them, right there in front of you!' They're not from another world'," he told The Daily.

Other pictures and videos from the campaign have also gone viral.

News agency Associated Press had to clarify a caption of a photo showing Mr Romney bending down to pose with schoolchildren, as one girl stood behind him with a shocked expression on her face.

After it was shared widely online with suggestions it appeared the girl was staring at Mr Romney's bottom, AP amended their caption to say: "A student, right, reacts as she realises Romney will crouch down directly in front of her and her classmates for the group photo."

A gallery of behind-the-scenes photographs from Mr Obama's presidency published on The Guardian website about a week ago was also shared widely.

It featured the famous shot of the President bending down to let the son of a White House staffer touch his head after the little boy asked whether their hair felt the same.

- Sydney Morning Herald