Beginning with Queen Victoria in the 17th century, posing for official photographs became an essential aspect to life as a member of the royal family.
"Photography provided a close look into royal family life, their domestic life," Charlotte Bolland, a senior museum curator at London's National Portrait Gallery, told The Guardian. "There was huge interest in the couple [Victoria and her husband, Prince Albert, who had nine children], and with photography, people could be brought into a faux intimacy with them."
As the centuries have gone on, the portraits have become more and more relaxed, with Bolland explaining, "The royal family is very aware of the images and what they are communicating."
For Queen Elizabeth II and Prince Philip's engagement photo, for example, the couple displayed a surprising amount of affection at the time, and they were the first couple to show off the engagement ring in their portrait. (It became a standard practice moving forward, with the portraits taking on a slightly less formal tone before William and Kate and Harry and Meghan's vastly more intimate offerings; the latter even released a candid from the photo shoot.)
Royals have long had portraits commissioned for engagements, weddings, birthdays and other major milestones, giving the public a rare peek behind the gates at life at Buckingham Palace. While celebrated photographers are usually commissioned to take the portraits, Kate has actually snapped the photographs for the majority of the official photos of her three children.