Afghans vote in a presidential election that marks the first democratic transfer of power since the fall of the Taliban in 2001.<br/> <br />The incumbent Hamid Karzai was among the early voters.<br/> <br />He's barred by the constitution from standing again after 12 years in power.<br/> <br />Eight candidates are battling it out to succeed him.<br/> <br />Of those, political observers say there are three front runners most likely to win.<br/> <br />Former foreign minister Abdullah Abdullah is one of them.<br/> <br />Zalmay Rassoul, also a former foreign minister, is another.<br/> <br />Ashraf Ghani, a former finance minister, is the third.<br/> <br />Voting is taking place amid tight security after Taliban threats to disrupt the polls through bombings and assassinations.
