[Breaking news update, Friday, 11:50 p.m. ET]
Iran's Supreme Leader, Ayatollah Seyyed Ali Khamenei, cast the first ballot in the country's presidential election on Friday morning. His vote marks the opening of the polls.
[Original story, posted Wednesday, 4:37 a.m. ET]
What's at stake in Iran's presidential election?
(CNN) -- More than 50 million Iranian voters are eligible to go to the polls Friday to pick a new president.
The country, a regional power player, faces a painful economic situation, resulting in part from international sanctions intended to pressure Tehran over its foreign policy stance and its nuclear program
The last presidential election, in 2009, sparked allegations of massive fraud and a protest movement that was subsequently crushed by the government of the re-elected President Mahmoud Ahmadinejad.
Friday's presidential vote thrusts Iran's democratic process back into the spotlight. But a question mark hangs over how much of a difference its outcome can make to the Iranian people.
How democratic is Iran's election process?
Iranian citizens ages 18 and over, male and female, can vote for the president, but only an Iranian-born male Shiite can run for president, said Alex Vatanka of the Washington-based Middle East Institute.
Those who want to stand have to be approved by Iran's Guardian Council, a non-elected body made up of six clerics and six lawyers operating under the oversight of the Supreme Leader Ayatollah Ali Khamenei. That means only candidates who have Khamenei's blessing can really contest the election, said Vatanka, making it "very much a limited, controlled process."
Khamenei "has four significant tools to weaken democratic institutions," and over time he has used them to sap the power of the president and parliament, said Mehdi Khalaji, a senior fellow at the Washington Institute for Near East Policy.
First, the judiciary are accountable to him and listen only to him, he said. The country's intelligence apparatus also answers to the Supreme Leader, as does Iran's military; he is commander-in-chief. Khamenei also pulls the strings when it comes to state-run TV and radio, allowing him to control the flow of information.
"Each election, he makes sure that all those who may cause problems for him or challenge his authority won't be qualified," Khalaji said, which means the outcome is effectively "pre-set."
The other obstacle to democracy is fraud, said Vatanka said, citing the disputed 2009 election.
The Guardian Council and Interior Ministry will be the chief bodies monitoring the vote, he said.
Who's running for election?
The Guardian Council approved eight candidates to run in the election, out of more than 680 who registered, but two of those dropped out of the race this week. The six remaining are: Mohammad Bagher Ghalibaf, Ali-Akbar Velayati, Saeed Jalili, Mohsen Rezaei, Hassan Rouhani, and Mohammad Gharazi.
Velayati, Ghalibaf and Jalili, who is Iran's chief nuclear negotiator, are all seen as being close to the Supreme Leader and would be unlikely to challenge his authority, said Khalaji.
The two who dropped out are Mohammad Reza Aref and conservative Gholam-Ali Haddad-Adel, who had not been polling strongly.
Aref, who was vice president to former President Mohammad Khatami, was seen as a reformist candidate. Khatami said he was backing Rouhani, seen as a centrist, and that Aref had withdrawn "to increase the reformist camp's chances of winning," according to Iran's state-run Press TV.
Rouhani did better than Aref in the presidential debates and seems to have the top guns behind him, including former president and political heavyweight Akbar Hashemi Rafsanjani, Vatanka said. One of the two had to drop out so the reformist camp would not split its vote, he added.
However, those voters who backed Aref will not necessarily back Rouhani, said Khalaji.
In a blow to Ahmadinejad, his aide and protege Esfandiar Rahim Mashaei was among those excluded from standing by the Guardian Council. Another high-profile figure barred from the race was Rafsanjani.
What's the difference between Iran's president and the supreme leader?
The Supreme Leader Ayatollah Khamenei holds many of the cards and, as an unelected individual, can claim the greatest share of power. He directs foreign policy and has a degree of economic control too.
Iran's president is the country's highest official after the supreme leader and is responsible "for implementing the Constitution and acting as the head of the executive, except in matters directly concerned with (the office of) the Leadership."
The president has a lot of sway over economic issues but not full control, said Khalaji.
Khamenei has sought to present himself as a religious figure who is above politics, said Vatanka, but his actions have betrayed his agenda. "He tends to opt for policies which are conservative and almost always about protecting his power," he said.
Iran has an elected parliament, but it does not play a significant role in deciding strategic issues such as foreign policy, said Vatanka, although it does pass a budget.
The Guardian Council again plays a role in approving parliamentary candidates, and lawmakers have seemed keen to support the supreme leader since he and Ahmadinejad fell out, he added.
"There has been a power grab over the past few years by Khamenei, and that has come at the expense not only of the president but of Parliament," Vatanka said.
What happened in 2009?
Ahmadinejad, who had Khamenei's backing, found himself in an unexpectedly close and polarized race with reformist candidates, including Mir Hossein Moussavi. People were so excited they rallied in the streets across the country, and the voting seemed set to go to a second round, Khalaji said.
However, Ahmadinejad won re-election with 62.63% of the vote, according to Iranian government sources. His nearest rival, Moussavi, received 33.75%. Demonstrations protesting the outcome of the election broke out across Tehran. Dozens of people were reported killed. Despite widespread unrest, Ahmadinejad's re-election was formally certified by the Guardian Council.
The Green Movement, the opposition force that exploded onto the scene during the 2009 elections, was later crushed by the regime's security apparatus. Moussavi and another opposition leader, Mehdi Karoubi, remain under house arrest.
Dozens of political activists are still in prison, and others who were released live under restrictions, Khalaji said.
Iran's security officials have warned the public against anti-government street protests this time round.
No independent investigation was allowed, said Vatanka, and the extent of the fraud that took place in 2009 remains unknown.
How is this election expected to differ from others?