Image copyright Reuters Image caption The singer of pop songs such as Shake It Off is expected to take the stand to testify

Pop star Taylor Swift is "absolutely certain" she was groped by a Colorado radio DJ, a court has heard.

Ms Swift, 27, accuses broadcaster David Mueller of slipping his hand under her dress while they posed backstage together at one of her 2013 concerts.

Her lawyer said in his opening statement at the court in Denver, Colorado, that Mr Mueller had "grabbed her rear end".

Mr Mueller sued the singer in September 2015, calling her allegation false.

He said she had cost him his $150,000-a-year job as a host at country station KYGO-FM.

Ms Swift - who was in court on Tuesday - countersued a month later, saying what occurred at the city's Pepsi Center was assault and battery.

On Tuesday, jurors were shown a photograph of the alleged assault at a VIP room meet-and-great before the gig on 2 June 2013.

In the picture, Mr Mueller and his then-girlfriend, Shannon Melcher, stand with Ms Swift in the middle.

All are smiling, and Mr Mueller's right hand is hidden behind the Shake it Off singer.

Mr Mueller's lawyer, Gabriel McFarland, said in his opening statement the image shows his client's hand "is not underneath Miss Swift's skirt, and her skirt is not rumpled in any fashion".

Image copyright Getty Images Image caption Fans waited for hours for a chance to get inside the courtroom

"David Mueller unequivocally denies he touched her inappropriately in anyway," Mr McFarland said as his client looked on in court.

"Falsely accusing someone of inappropriate touching is equally offensive, equally wrong and should not be tolerated."

In his opening statement, Mr Mueller said he had only sued "to clear his name and for lost earnings", denying reports that he was seeking $3m in damages from the radio promotions director of his former station.

But Ms Swift's attorney, Douglas Baldridge, said Mr Mueller had given seven accounts of what happened.

He had also destroyed taped conversations about the incident with his bosses, said the lawyer.

Mr Baldridge told the eight jurors: "What's wrong with this picture? A woman gets assaulted, a woman reports it, and she gets sued."

He added: "It's not inappropriate touching. It's assault."

On 3 June, Mr Mueller met his bosses. He was fired the next day on the basis he had violated a "morals clause", according to Mr McFarland.

Ms Swift, who was 23 at the time of the incident, is suing Mr Mueller for the symbolic amount of $1.

She was accompanied in court by her mother Andrea.

Ms Swift also attended jury selection on Monday.

Her fans, known as Swifties, waited outside court from the early hours for a chance to get one of the court's 32 public seats.