Flip open a school yearbook and you’ll find a window into the past. The often awkwardly-posed photographs offer enough clues about trends of bygone years that data scientists are now looking to those annual publications for information. One of the first efforts to do so points to one peculiar finding: Students have become more smiley over the years.
An analysis of nearly 38,000 American high-school yearbook photos from the 1900s to the 2010s shows the gradual shift from serious to lighthearted expressions, reports Steve Dent for Engadget. Average hairstyles and fashion can also be gleaned from the composite images created by researchers at the University of California, Berkeley.
The team analyzed 949 scanned yearbooks for senior-class portraits. They grouped the photos by gender and decade to create the average face and expression for each period. The algorithm they used also identified styles corresponding to each decade: Curly bangs for women in the 1940s, flipped hair for women in the 1960s and long straight styles of recent years. (Sorry guys, your hair is rather static.) The algorithm was even able to identify unclassified portraits by the decade in which they were snapped. Also visible in the composite photos is the gradual increase in racial diversity. The researchers point out that African Americans were not well-represented in high schools until the middle of the 20th century.
From all these data, smiles in particular stood out. The researchers were able to quantify the intensity of smiles by measuring lip curvature. That "smile intensity metric" showed that women consistently smile more than men and everyone sports bigger smiles in recent years. Whether or not modern people are happier is up for debate, but we sure look it.
The smile trend isn’t surprising: Early photography required people to sit still for the long exposure times, so dour expressions are the norm rather than toothy grins. The formality of sitting for a rare portrait also contributed to the serious faces early on. In a 2011 article from The Economic Times, Christina Kotchemidova notes that photographers in British studios initially told their subjects to say "prunes" rather than "cheese," to get a pursed-lips look rather than a toothy smile.
The purpose of the new study, however, wasn’t to look for changing expressions, but rather to demonstrate the ways that pictures can be mined for data.
The adage "an image is worth a thousand words" holds true in historical research, the researchers write in a paper about their work, published at arXiv.org. "For example, it would be hard for a future historian to understand what the term 'hipster glasses' refers to, just as it is difficult for us to imagine what flapper galoshes might look like from a written description alone."
Adds lead author Shiry Ginosar in an article by Inga Ting for The Sydney Morning Herald: "Yearbooks are a cool set of data as they give us kind of a 'peephole' into the past where everything - pose, the reason for taking the picture, the age of the subjects etc. - remains constant, except for the passing time."