A convicted rapist found a mobile phone then threatened to send nude images of its owner to her friends.

Andrew Allan, 43, appeared at Stirling Sheriff Court, where it was heard a 20-year-old student had either lost her phone or had it stolen while on a night out in Falkirk in October 201

She cancelled her contract but did not report the loss to police.

The phone contained "various pictures" she had taken of herself and sent to her boyfriend.

On a Sunday about two months later, she received an email from Allan, who was a stranger to her, with the subject line: "I know all about you".

The message read: "Maybe I'll send the acid tab video to your mum and the naked ones to people on your friends list. I wrote it all down.

"What's it worth to keep them all private? Get back to me soon or I'll start posting."

Allan added a warning the woman should not tell anyone and attached some of the images to the email.

Prosecutor Lindsey Brooks said Allan's victim was "alarmed and distressed" and sent private Facebook messages to her friends asking for advice.

A little later she received another email from Allan, with the subject line: "Not off to a good start".

It read: "I told you not to tell anyone. Last chance - tell anyone that replies that you were kidding or I'll start posting."

The woman then went to the police, who traced the emails to Allan via his IP address.

Officers raided Allan's home in Grangemouth, found the woman's missing phone in a kitchen drawer and arrested him.

Allan, a cleaner, pleaded guilty on indictment to contravening Section 6 of the 2009 Sexual Offences (Scotland) Act by intentionally causing the woman to look at a sexual image.

Sheriff Wyllie Robertson told Allan his behaviour had to be seen against his background of "extreme sexual violence".

He said a custodial sentence was the only appropriate disposal and sentenced Allan to two and a half years as part of a seven-and-a-half year extended sentence.

In 2003, Allan, then a waiter, was jailed for four and a half years for raping a 30-year-old hotel guest in the Covenanters' Inn in Aberfoyle, Perthshire.

Five years later, he was banned for life from making sexual advances to women when he has consumed alcohol.