Pippa Middleton could escape being drawn into a police inquiry unless a formal complaint is lodged over pictures which show her being driven through Paris by a friend apparently brandishing a handgun.
French police said they cannot launch an investigation based on the strength of the photographs alone which have sparked an outcry on both sides of the Channel.
They will only probe the matter further if a potential witness comes forward or the photographer presents officers with evidence.
Prince William's sister-in-law found herself at the centre of controversy after she was pictured in the French capital on Saturday.
The 28-year-old had been in Paris for a lavish fancy dress party to celebrate the 30th birthday of fashion entrepreneur and aristocrat Vicomte Arthur de Soultrait.
Images taken a day later show her travelling in an Audi convertible while the driver points what seems to be a pistol at the photographer.
France is still reeling from a string of gun massacres but police in the capital insist they are currently taking no action over the photographs.
"We don't know the circumstances in which these photographs were taken," a source said.
"But we cannot launch an inquiry based simply on photographs that have appeared online and in the press. There would need to be a witness but at the moment there is nothing.
"To launch an investigation, it would be necessary for there to have been a complaint or something would need to have presented itself to police.
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"A photograph cannot launch an investigation. In this case, there are just the photographs. No one was injured and nothing more happened. There is nothing to this affair, at the moment, as far as police are concerned."
If detectives opened an inquiry into the pictures, they would "logically" want to quiz Miss Middleton, police said.
De Soultrait, who can be seen in the photographs sitting in the back of the vehicle, could also be questioned.
But police stressed there was currently nothing to suggest this was likely.
The 28-year-old sister of the Duchess of Cambridge was reportedly being driven to the Gare du Nord station to board a Eurostar train to London when the photos were taken.
The previous evening, she and other guests attended de Soultrait's exclusive celebration entitled "Le roi est mort, Vive le vicomte".
The party saw friends turn out in an array of elaborate period costumes, with Miss Middleton sporting a bright pink and gold number with flared sleeves.
De Soultrait is the man behind the Vicomte A label which produces preppy clothing and sportswear.
The images emerged after a series of fatal shootings which rocked France this year.
Last month a rabbi and three children were gunned down outside a school in Toulouse.
They were killed with the same .45 automatic pistol used in two attacks in which three soldiers of North African and Caribbean origin were murdered in the region a week earlier.
On March 10, a gunman on a scooter shot and killed a paratrooper in Toulouse and, days later, an attacker, also on a scooter, opened fire on three uniformed paratroopers at a bank machine in Montauban, about 30 miles from the city, killing two and critically wounding the third.
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