The Duke and Duchess of Cambridge authorised an open letter to be issued to the world media by Kensington Palace urging restraint from publishing unauthorised pictures of the little prince and princess.
"I am writing to provide an overview of the current challenges facing Kensington Palace as we seek to protect Prince George and Princess Charlotte from harassment and surveillance by paparazzi photographers.
"The Duke and Duchess of Cambridge have expressed their gratitude to British media organisations for their policy of not publishing unauthorised photos of their children.
"This stance, guided not just by their wishes as parents, but by the standards and codes of the industry as it relates to all children, is to be applauded," it adds.
The palace says photographers have hidden themselves in car trunks, obscured themselves in sand dunes, and used other children to take pictures of Prince George.
Prince William, 33, the second in line to Britain's throne, has always believed paparazzi photographers in Paris were ultimately responsible for his mother Princess Diana's death in 1997, when her car crashed in an underpass, trying to escape photographers on mopeds.
The letter reads: "It is of course upsetting that such tactics - reminiscent as they are of past surveillance by groups intent on doing more than capturing images - are being deployed to profit from the image of a two-year-old boy.
"The worry is that it will not always be possible to quickly distinguish between someone taking photos and someone intending to do more immediate harm," it added.