The publisher of the Sun newspaper has filed a High Court legal action against ITV and ITN over the use of video showing the Princess of Wales at a farm shop in Windsor.
The footage, obtained by The Sun, showed Kate and the Prince of Wales in public after her surgery, amid her absence from public life.
A filing to the Intellectual Property and Enterprise Court was made by News Group Newspapers Limited against ITV and ITN on Monday.
A spokeswoman for the broadcaster and news company said: “ITV and ITN will strongly resist this claim.”
It is understood by the PA news agency that the claim relates to the video, in which Kate is seen at Windsor Farm Shop, close to her home, Adelaide Cottage.
The footage from March 18 shows the princess with her hair down, wearing a black jacket and leggings, chatting with William and carrying a large white bag.
Kate has been away from official duties after her abdominal surgery in January.
On March 22 she announced that cancer was discovered during post-operative tests and she is now undergoing chemotherapy.
Before the Sun footage, the Princess of Wales was photographed for the first time near Windsor Castle on March 4 in the passenger seat of a car, according to TMZ.
Last month, Kate issued a public apology when an image of her and her children, released for Mother’s Day, was found to have been digitally altered.
It fuelled the escalating conspiracy theories online about her health and whereabouts, after it was withdrawn by picture agencies over concerns it had been manipulated.
On Tuesday, the princess was made a Royal Companion of The Order of the Companions of Honour by the King for her public service and support of the arts.
NGN declined to comment.