(Incident at 4:38 mark)
The rally was clearly an eventful one - other images showed a naked man being led away in handcuffs by police.
It is not clear if the man was involved in the book-throwing incident - or why he was not wearing any clothes.
The bizarre incident recalled the moment in 2008 when an angry Iraqi journalist hurled a shoe at then-U.S. President George Bush during a press conference in Baghdad.
The surprisingly nimble Mr Bush ducked the shoe - and the moment became immortalised with online parodies and internet video games.
But the incident was also marked with controversy as U.S. media questioned why the Secret Service - whose members are supposed to be willing to take a bullet for the President - were not close enough to Mr Bush to deflect the attack.
It is expected that the same questions will be asked about yesterday's incident.
It came as Mr Obama tried to rally voters in Phildelphia to use to three weeks left before congressional elections to go to the polls.
The president relied on an oft-used speech as he addressed the crowd in the city's Germantown community with the driving cadences that swept him into the White House two years ago.
He and the Democratic party know, however, that this year finds Democrats imperiled because of what has become known as the 'enthusiasm gap', with party voters expected to stay away from the polls.
That could be disastrous in a nationwide vote that was widely believed to hand the majority in the House of Representatives and, perhaps, the Senate to Republicans.
There are ample reasons for Republican optimism. Poll after poll shows deep voter discontent and even anger at Mr Obama's and congressional Democrats' leadership. Mr Obama and his fellow Democrats are being blamed for the slow economic recovery and continuing high unemployment.
On Friday, the Bureau of Labor Statistics - in the last major economic news before the November elections - delivered another painful blow to Democrats: The U.S. lost 95,000 jobs in September and unemployment remained stubbornly stuck at 9.6 per cent.
In another complication for Democrats, the government is expected to announce this week that more than 58 million Social Security recipients will go through another year without a cost-of-living increase in their monthly benefits.
It would mark only the second year without an increase since automatic adjustments for inflation were adopted in 1975. The first year was this year.
'I think the pundits are wrong. I think we're going to win. But you've got to prove them wrong,' Mr Obama said, jabbing his finger toward the audience.
'They're counting on you staying home. If that happens they win.'
Vice President Joe Biden joined Obama at the rally.
Democrats are desperate to fire up their base and win back independent voters against the likelihood that Republicans will grab the majority on November 2 and create a more hostile Congress that could cripple Mr Obama's efforts to implement his agenda in the last two years of his term.
The President sometimes sounds wistful when noting the differences between this year and 2008, an he remarked again on Sunday about the extraordinary political high that he and his supporters felt after his victory.
First Lady Michelle Obama recently told Democratic supporters that the big-stadium events of 2008 were 'very exciting, and people should know that those rallies invigorate Barack as well'.
'It's time for us to re-engage that energy,' said the First Lady, who plans to campaign with her husband later this month.
Republicans need to pick up 40 seats to win power in the House and would need to gain 10 seats in the Senate to take control from the Democrats.
Governing parties typically lose seats in U.S. midterm elections, which take place in the middle of a president's four-year term. But polls indicate that Democratic losses are likely to be particularly severe.
It get's even better teehee!
Someone Finally Streaked in Front of President Obama for $1 Million
It took almost two whole months for someone to take up British billionaire Alki David on his offer of $1 million for the first person to streak in front of President Obama with the name of David's website, Battlecam.com, written across his or her body, while shouting "Battlecam.com!" six times. (This is how billionaires spend their money, after the yachts and women lose their entertainment value.) Considering the many public appearances that Obama makes, and the general lack of shame among many in the American populace, two months is a surprisingly long time.
But the wait is over, thanks to 24-year-old Juan Rodriguez, who stripped naked at Obama's Philadelphia rally yesterday. He was assisted by two dudes from The Howard Stern Show, who filmed it. And David appears ready to uphold his end of the bargain, once the video confirms that Rodriguez fulfilled all the requirements. "This is the first time anybody has attempted it," he told the Daily News."I still don't know if he was successful. If he has done it, I'll pay him in cash."
So really, everybody wins here. Once he's released from jail, Rodriguez will be a rich man. David's Battlecam.com, where live webcam feeds are voted on by viewers, will get publicity in major news outlets around the world and on Daily Intel. The only person who seems to have lost out in the endeavor is this woman, who was so disgusted by the sight of Rodriguez's naked body that she needed a hat, sunglasses, and two hands to shield it from her peripheral vision.
Obama streaker, Juan Rodriguez, got naked at rally for $1M prize promised by billionaire Alki David [NYDN]