There are already a lot of videos circulating that show vote-flipping, where you vote for A, but the machine records B. Making selfies illegal would make the evidence that this has happeened inadmissable in court.
Are you a cop by any chance? Because you do not understand the rules of evidence. Evidence gathered by a citizen during the commission of a crime is still admissible in court. It's evidence gathered by a police officer that isn't.