SINGAPORE - On Facebook, Alvin Yeo Pei Jin identified himself as "Happy Tan" and used the picture of a good-looking Taiwanese man, instead of his own.

The canvas maker, 49, did this to court women, but he had a specific target. He was on the prowl for middle-aged women with long hair. Once he found someone he fancied, he added them as friends and initiated chats.

It did not take long before the chats progressed to the mobile phone where he would ask for their nude pictures. But once he was armed with that, Yeo threatened to expose the women unless they had sex with him.

Yeo was jailed for 13 months on Friday (Nov 10), after pleading guilty to five charges, including mischief and insulting the modesty of a woman. Ten other charges were taken into consideration in sentencing.

One of his victims was a 48-year-old woman who was known to his family.

After receiving his Facebook message in June 2016, she started chatting with Yeo, who claimed to be a widower living in Redhill with two children. They subsequently exchanged telephone numbers and continued chatting through WhatsApp.

When she sent pictures of herself to him, he recognised her to be someone known to his family. But that did not deter him.

He still got her to send over nude pictures, and she did so over the next few days.

After receiving them, he wanted to have sex with her but hesitated because he looked different from his Facebook profile picture.

So Yeo devised a plan to force the victim to find five men to have sex with, hoping that he would eventually be one of them.

From June 14 to 15, 2016, he sent her multiple WhatsApp messages to harass her.

Among other things, he threatened to expose her pictures to others, including her friends and relatives, if the victim blocked him. He also threatened to place her nude pictures outside her home so her husband would see them.

The victim was shocked by his messages, especially since she had not revealed any of her personal particulars to him. She blocked him on Facebook and WhatsApp, and made a police report.

A few days later, she made another report when she found an A4-size paper with a full frontal nude picture of herself on it, but with her face torn off. The picture was pasted at the gas meter outside her home. She immediately took it down.

Investigations showed that Yeo made such threatening communication by pasting the paper with the victim's nude picture and the message - "Still block me, I will... we will see" - at the gas meter to harass her.

The victim's son returned home that evening and found another piece of paper stuck on the wall. A message in Chinese stated: "Tomorrow if you don't reply my message, I will post your big face at the door there".

The victim made a further report. Yeo was arrested on Sept 19 last year.

Yeo's lawyer James Ow Yong said his client has two children, and his wife is suffering from degenerative diseases and has been using a wheelchair for about four years.