A French court will rule later on a bid by the Duke and Duchess of Cambridge to stop the sale and distribution of topless pictures of the duchess.
In court in Nanterre near Paris on Monday, the couple's lawyer said the photos' publication by French magazine Closer had breached their privacy.
The royals want Closer to hand over the images, to prevent further publication, or face a daily fine.
A lawyer for Closer claimed the royal couple's reaction was disproportionate.
After first appearing in Closer last week, the pictures were used on foreign websites, in the Irish Daily Star and most recently, in Italian gossip magazine Chi.
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The three magistrates presiding over the civil case in Nanterre are expected to announce whether an injunction will be granted at 11:00 BST on Tuesday.
In court on Monday, Aurelien Hamelle, the lawyer representing Prince William and Catherine, said the scenes captured were intimate and personal and had no place on the front page of a magazine.
He said the couple could not have known they were being photographed, adding it would only have been possible to see them with a long lens.
If the original digital images were not handed over, the company that owned Closer should face a fine of 10,000 euros (£8,000) for each day of non-compliance, he argued.
In response, Delphine Pando, representing Closer, said that topless photographs were no longer considered shocking in modern society.
Ms Pando denied that the chateau where the couple had been sunbathing was inaccessible to public view. She also said the magazine did not hold the rights to the pictures, so it could not be proved that the magazine intended to republish them.
The BBC's Paris correspondent Christian Fraser said most lawyers seemed to agree that under strict French law the pictures represented an undisputed breach of privacy - an open-and-shut case.
Under French law, the damages related to legal proceedings could run into tens of thousands of euros and, in theory, the magazine editor and photographer could be sent to jail for a year.
Closer editor Laurence Pieau has already defended publication, insisting the photos were not in the least bit shocking, and has suggested that she has more intimate photos not yet published.
Italian magazine Chi - along with Closer, part of former Italian prime minister Silvio Berlusconi's Mondadori media group - printed a special edition featuring more than 20 pages of the photographs.
It carries a picture of the duchess, topless, on its front cover with a headline that reads: "The Queen is Nude!"
In an editorial the magazine's director, Alfonso Signorini, said he considered the photographs of the duchess to be "normal and up to date with the times".
They were "not particularly sensationalistic nor damaging to her dignity" and "surely makes her more likeable" and "less distant from all of us", he wrote.
Internal investigation
Meanwhile, Irish Daily Star editor Michael O'Kane has been suspended while an internal investigation is carried out into the publication of the photographs.
The paper's co-owners - Britain's Northern and Shell group and the Dublin-based publisher Independent News and Media - have condemned the decision, saying they had no prior knowledge of it.
Richard Desmond, chairman of Northern and Shell, said he intended to withdraw from the Republic of Ireland and had begun steps to close down the joint venture.
A source at the Irish Daily Star said the belief there was that Northern and Shell would pull out of the publication on Tuesday, when a board meeting of the paper is scheduled to take place.
No British newspaper has printed the pictures, with the Daily Mail saying it had been offered similar pictures last week but had rejected them and the Sun saying that no responsible newspaper "would touch them with a bargepole".
The photographs were taken while the duchess was sunbathing on a private holiday with her husband at the French chateau of the Queen's nephew, Lord Linley, in Provence.
Currently on a Diamond Jubilee tour of South-east Asia and the South Pacific, the royal couple travel on Tuesday to the tiny island nation of Tuvalu.
-BBC