The photos you post on social media may be saying more about you than you intend. Scientists from Harvard University and the University of Vermont have found that there is a strong correlation between the nature of photos posted on Instagram and the poster’s mental health. The link is so strong that researchers Andrew Reece and Chris Danforth suggest the algorithm they devised could be used for early detection of mental illness.The experiment started with recruiting 500 test subjects from Amazon’s Mechanical Turk platform, who also used Instagram. They were asked to complete a standard clinical depression survey and share their Instagram posts for analysis. Only 170 agreed to be part of the test, and 70 of them showed some level of depression based on the survey.When the researchers downloaded the images provided by the study participants, they were left with a whopping 40,000 images to dig through. The analysis was based on the last 100 images posted by healthy people, and for those with depression the last 100 posted before their diagnosis. This was done to eliminate the effect of treatment on the images posted.Reece and Danforth used a different set of Turk workers to rate the photos, then added objective measurements like average hue, color saturation, contrast, and the number of faces visible. The reaction of other Instagram users in the form of likes and comments was also taken into account. The model was able to reliably predict which users were clinically depressed based on these metrics.Depressed people tended to post photos with predominantly blue, black, and gray color palettes. They also received fewer likes on Instagram than healthy individuals. Depressed people also had a strong preference for the Inkwell filter, which adds a monochrome effect to photos. Meanwhile, healthy individuals were more likely to use the Valencia filter, which lightens the colors. Faces were more common in the photos submitted by depressed users, but usually only one face — their own. So, excessive selfie use is associated with depression now.When tested with a new group of individuals, the researchers reported that it correctly identified 70% of those with depression. That’s better than most general practice doctors can do. Maybe some day the apps on your phone will start asking how you’re feeling based on the photos you post.