Updated

Barack Obama complained on Wednesday about an Internet photo that claims the Democratic presidential candidate didn't hold his hand over his heart during the Pledge of Allegiance.

"This is so irritating," Obama said when asked about the photo in Muscatine, Iowa.

The photo, which has circulated widely on the Internet, was taken in September during Iowa Sen. Tom Harkin's annual Democratic fundraiser. A message accompanying the photo claims Obama didn't observe the pledge.

Obama said the photo was taken during the singing of the national anthem, not the pledge.

"My grandfather taught me how to say the Pledge of Allegiance when I was 2," Obama said, his annoyance obvious. "During the Pledge of Allegiance you put your hand over your heart. During the national anthem you sing."

A woman also asked Obama about the photo Tuesday night during a town hall meeting in Cedar Rapids, evoking a similar reaction.

"This is the classic dirty trick of the campaign," Obama said.

He added that he's often the target of anonymous criticism on the Internet.

"You've got e-mails saying I'm a Muslim plant trying to take over America," Obama said. "We've seen this before."

He advised the woman to tell the sender of the e-mail the real story.

"You don't have to curse them out, just tell them they've got their facts wrong," he said.