If Instagram had existed during the Victorian era, selfies would probably contain a lot more prune-face than "duckface." By the mid-19th century, camera technology was still in its infancy, and exposure took several minutes. Beginning at the first British photo studio in 1841, as academic Christina Kotchemidova discovered, photographers would request patrons to say "prunes" instead of "cheese" to make them purse their lips together. Natural-looking wide-mouthed grins would've been harder to capture on film since subjects would have to hold the pose perfectly still for an uncomfortable amount of time (ex. the daguerreotype, invented in 1839, revolutionized photography with its lightning-fast exposure time of...15 minutes). Moreover, smiling in photos wasn't commonplace until Kodak democratized picture-taking in the 20th century.
People's serious expressions in early photos was a holdover from portraiture. Nicolas Jeeves at The Public Domain Review explains how, logistically, maintaining a smile during a portrait session isn't feasible, and especially not for creating a natural-looking painting (my cheeks hurt just thinking about it). And although the lackluster dentistry of the day might've been a contributing factor to folks not caring to bear a toothy grin in the early days, Jeeves suspects the unsmiling poses have more to do with how the expressions were perceived through a socioeconomic lens. "A person who wished to appear dignified and respected certainly wouldn't have said "cheese" because grinning was considered the expression of a drunkard, pauper, or paid entertainment," he writes.
Even Mark Twain, a fellow who made his mark with literary humor and entertainment, resisted revealing his goofier side in photographs -- though ironically, Huckleberry Finn is the only character depicted with a "toothy smile" in 19th-century illustration art. He even once wrote to the Sacramento Daily Union that, "A photograph is a most important document, and there is nothing more damning to go down to posterity than a silly, foolish smile caught and fixed forever."
But in 1900, as the Victorian era was coming to a close, people would soon begin smiling in more pictures with the arrival of the $1 Kodak Brownie camera. Mental Floss details how Kodak's marketing campaign and companion how-to photography books and pamphlets essentially trained the emerging American middle class to start snapping pics, and often the photographers in Kodak advertisements were depicted wearing delighted grins, which helped replace portrait photography's stoicism with a happier-go-lucky camera culture. What remains unknown is whoever tossed out the prunes of photo yesteryear and replaced it with the enduring "say cheese," which cemented the smile's central role in 20th-century photography.