Jared James Abrahams entered his plea Tuesday in federal court in Orange County. He faces up to 11 years in prison and fines of up to $1 million when he's sentenced in March.
Abrahams also is accused of emailing the victims and saying he'd publish the images of them on social media sites if they didn't send him nude photos or undress for him.
He told the judge he has autism and has been under treatment for it for the past 10 years.
Abrahams agreed to plead guilty last month to three counts of extortion and one count of unauthorized access of a computer.