The images of Meghan emerged on Monday morning and showed her walking her two pets with her son in a baby sling in a park in Vancouver.
But the pictures were reportedly taken by photographers hiding in bushes with long-lens cameras.
After the images surfaced, the couple’s team of lawyers at Schillings sent a legal notice to the UK press, TV and photo agencies warning against using them.
The pictures appeared on the front page of the The Sun newspaper as well as digital outlets such as MailOnline.
Prince Harry rejoined his wife in Canada on Monday evening after hashing out the new arrangement for the two of them with other senior members of the royal family.
He had not seen his wife or his young son for 10 days during the talks.
The letter from the law firm said: “There are serious safety concerns about how the paparazzi are driving and the risk to life they pose.”
Harry has repeatedly compared the treatment of his wife at the hands of the press to that of his mother who was killed in a car crash in Paris while being chased by the paparazzi in 1997.
On Sunday evening, at an event for his Africa-based youth mental health charity Sentebale, he described the media as “a powerful force” in a speech.
He said: “I was born into this life, and it is a great honour to serve my country and the Queen.
“When I lost my mum 23 years ago, you took me under your wing.
“You’ve looked out for me for so long, but the media is a powerful force, and my hope is one day our collective support for each other can be more powerful because this is so much bigger than just us.
“It has been our privilege to serve you, and we will continue to lead a life of service.”
Following the talks to renegotiate the Sussexes’ relationship with the royal family, the Queen said she was “pleased that together we have found a constructive and supportive way forward for my grandson and his family”.