A Playboy model pleaded not guilty today to a charge of invasion of privacy over a picture she secretly took and posted on social media of a nude 70-year-old woman at a gym.

Dani Mathers, who was the magazine's 2015 Playmate of the Year, faces up to six months in jail and up to a $1,000 fine over the picture that she posted on Snapchat in July, drawing a storm of criticism.

The photo showed the naked woman from behind at a Los Angeles area fitness centre with a mocking caption that read: "If I can't unsee this then you can't either."

A lawyer for Mathers, who did not appear in court on Monday, said his 29-year-old client felt bad about her actions.


"She very much regrets what happened," Tom Mesereau told reporters outside the courthouse.

"She apologised for her behaviour and we're looking forward to resolving this case in a very fair manner."

Mathers was banned from LA Fitness gyms after the incident that sparked a public outcry and raised questions about body shaming, especially on social media.

She also reportedly lost her job on a radio talk show.

"Body shaming is humiliating, with often painful, long-term consequences," prosecutor Mike Feuer said when the misdemeanor charge of invasion of privacy was filed in November.

"While body shaming, in itself, is not a crime, there are circumstances in which invading one's privacy to accomplish it can be. And we shouldn't tolerate that."

Mathers apologised after uploading the image, saying that it was meant to be shared as a private message but was posted publicly.

"I'm sorry for what I did... I need to take some time to myself now to reflect on why I did this horrible thing. Goodnight," she said in a message on Twitter.

A pretrial hearing in the case is set for December 21.