A man who feared his former model-girlfriend had got together with her boss posted a topless photograph of her on the agency's Facebook page.
Kwek Jian Zong, 25, was jailed for three months yesterday and also fined $30,000 for helping an unlicensed moneylender.
A court heard how he took sexually explicit pictures of his girlfriend during a three-year relationship and threatened to circulate them online when she refused to have sex with him.
Deputy Public Prosecutor Suhas Malhotra said Kwek had been romantically involved with her since 2008. He had memorised her Facebook password while standing behind her one day in June 2010, after which he logged into her account several times.
She started work at the model agency in October that year and their relationship soon started to deteriorate.
They split in August 2011, after Kwek told his girlfriend - who cannot be identified - to quit the job and break up with the 52-year-old agency owner.
On November 29 that year, he posted a photograph of her breasts, though not her face, on the model agency's page.
The agency owner lodged a police report the next day.
Kwek admitted to three charges yesterday - transmitting an obscene object by electronic means, gaining unauthorised access to his ex-girlfriend's Facebook account and helping a loan shark to carry out electronic fund transfers between May and September 2013.
District Judge Jasvender Kaur said Kwek had victimised the woman using something given in intimacy as a weapon to violate her privacy.
DPP Suhas said Kwek agreed to work for an unlicensed moneylender called Adrian in May 2013 after he could not repay a loan.
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