The photos you post on Instagram can contain telltale visual clues that help predict if you're suffering from depression, a new study reports.

Computer software designed to scan photos for these hidden signals accurately diagnosed people with depression seven out of 10 times, said lead researcher Andrew Reece. He's a graduate student with the Harvard University psychology department.

"Depressed individuals in our study posted photos that were bluer, darker and grayer, compared to the posts of healthy participants," Reece said.

"Depressed people also tended to prefer Instagram's Inkwell filter, which turns a color image into black-and-white, whereas healthy participants preferred the Valencia filter, which gives photos a warmer, brighter tone," he noted.

In other words, people with depression were more likely to choose a filter that drained all the color out of the images they wanted to share, the researchers concluded.

Photos posted by depressed people also contained fewer faces, possibly because they aren't as likely to engage in lots of social interaction, the report pointed out.

The computer program's detection rate proved more reliable than that of primary care doctors, according to the study authors. Earlier studies have shown that general practitioners correctly diagnose depression in patients about 42 percent of the time.

"It's clear that depression isn't easy to diagnose, and the computational approach we've taken here may end up assisting, rather than competing with, health care professionals as they seek to make accurate mental health assessments," Reece said.

Years of prior research have established that depressed people are more likely to prefer darker or paler colors, said Dr. Igor Galynker. He is associate chairman for research at Mount Sinai Beth Israel's psychiatry department in New York City.

"There are reasons why depression is called blue, and why people associate red with raging, and why people say depression is like a dark or black cloud," Galynker said. "Patients with depression choose to wear darker colors. They generally avoid bright stimulation altogether."

Given that, it makes sense that such visual clues would show up in the photos people post on social media sites like Facebook or Instagram, Reece and his co-author, Chris Danforth, reasoned. Danforth is a professor at the University of Vermont College of Engineering and Mathematical Sciences.

To test their theory, Reece and Danforth asked 166 people to share their Instagram feed and their history of mental health. The team wound up collecting almost 44,000 photos from these volunteers, as well as responses to individual questionnaires assessing their level of depression.

The investigators then evaluated the photos using software programmed to look for known visual signs of depression.