As AllThingsD mentions, a whole bunch of voters — likely unaware of the relevant laws in their regions — are snapping photos of their completed ballots on election day and sharing them online. States including Florida, Georgia, Kentucky, Michigan, Nevada, North Carolina, and Texas prohibit taking photographs or recordings inside polling places. And some states, like Wisconsin, have harsh penalties for violators: as NBC 15 reports, the Democratic and Republican party chairs in the state had to remove photos of their ballots that they posted online after learning that doing so is a Class I felony with a punishment of up to 18 months in prison and a $10,000 fine.
Of course, restrictive laws on election day weren't created just to spite citizens, and were primarily designed to prevent voter intimidation — but with a camera in nearly every pocket these days, some overly restrictive measures may be a bit out of date. Not all states have such strict laws, and if you're intent on bringing your camera to the polls, be sure to check out the Citizen Media Law Project's 2012 guide to documenting the election.